TW201531156A - Low cost LED driver with improved serial bus - Google Patents

Abstract

An LED driver IC for driving external strings of LEDs comprises a prefix register and a data register connected in series with each other and with the prefix and data registers in other driver ICs. The prefix and data registers of the driver ICs are connected in a daisy chain arrangement with an interface IC. The interface IC loads data identifying a functional latch into the prefix register and data defining a functional condition into the data register of each driver IC. The data in the data register is then transferred to the functional latch to control the functional condition within the LED driver IC.

Description

Low cost LED driver with improved sequence bus

This invention relates to semiconductor devices and circuits and methods for driving LEDs in lighting and display applications.

The present application claims priority to Provisional Application No. 61/550,539, filed on October 24, 2011.

This application is related to the following applications, the entire contents of each of which are hereby incorporated by reference: Application No. 346, 625, filed on Jan. 9, 2012, entitled "Serial Lighting Interface With Embedded Feedback", No. 13/346,659.

LEDs are increasingly being used to replace lamps and light bulbs in lighting applications that include white light as one of the backlights in color liquid crystal displays (LCDs) and high definition televisions (HDTVs). When the LED can be used to evenly illuminate the entire display, performance, contrast, reliability, and power efficiency are improved by using more than one LED string and driving each string to a different brightness corresponding to one of the portions of the display illuminated by the particular LED string . "Regular dimming" means that the backlight system can perform this non-uniform backlight brightness. These systems can save up to 50% in power compared to LCDs with uniform backlighting. Using area dimming, the LCD contrast ratio can be close to the contrast ratio of the plasma TV.

In order to control the brightness and uniformity of light emitted from each LED string, specific electronics must be used. The driver circuit precisely controls the LED current and voltage. For example, one of the "m" LEDs connected in series requires an LED string equal to about 3.1 to 3.5 (typically 3.3) times the "m" for continuous operation. Supplying this necessary voltage to a LED string typically requires a step-up or step-down voltage converter and regulator called a DC to DC converter or a switched mode power supply (SMPS). When several LED strings are powered by a single SMPS, the output voltage of the power supply must exceed the highest voltage required by any of the LED strings. Since the highest forward voltage required is not known in advance, the LED driver IC must have sufficient intelligent functionality to dynamically adjust the power supply voltage using feedback.

In addition to providing the appropriate voltage to the LED string, the backlight driver IC must accurately control the current conducted in each string within a tolerance of ±2%. Accurate current control is necessary because the brightness of an LED is proportional to the current flowing through it, and any substantial string-to-string current mismatch will become apparent due to changes in the brightness of the LCD. In addition to controlling this current, regional dimming requires precise pulse control of the LED illumination in both timing and duration to synchronize the brightness of each backlight region, zone or block with the corresponding image in the LCD screen.

The prior art solution to the need for regional dimming limits display brightness and is expensive. For example, early attempts to integrate LED driver circuits with multiple channels of high voltage current sink transistors were problematic because of the mismatch in the forward voltage of the LED strings resulting in excessive power consumption and overheating. Attempts to minimize power consumption by reducing the current in these LEDs and limiting the number of LEDs that are proven to be uneconomical in a string (for better channel-to-channel voltage matching) require more LED strings and more A large number of LED drive channels. Therefore, the fully integrated approach to LED backlight driver systems has been limited to small display panels or very expensive "upscale" HDTVs.

Subsequent attempts to reduce overall display backlighting costs by using multi-wafer methods have sacrificed the necessary features, functionality, and even security.

For example, the prior art multi-chip system for driving LEDs shown in Figure 1 includes The backlight controller IC 6 of the plurality of discrete current slot transistors 4A to 4Q and the high voltage protection devices 3A to 3Q is driven. The backlight includes 16 LED strings 2A to 2Q (collectively referred to as LED strings 2). Each of the LED strings 2A to 2Q includes "m" LEDs connected in series. In practice, the number of LEDs in each string can range from 2 to 60. The current of each LED string is controlled by one of the discrete current slot MOSFETs 4A to 4Q, respectively. The backlight controller IC 6 sets the current in each of the LED strings in response to an instruction from a backlight microcontroller μC 7, which is communicated through a high speed, expensive sequence peripheral interface (SPI) bus bar 12. The microcontroller μC 7 receives video and video information from a scalar IC 8 to determine the appropriate illumination required for each of the LED strings 2A through 2Q.

The LED strings 2A through 2Q are powered by a common LED power supply rail 11 that is biased by a switched mode power supply (SMPS) 9 with a voltage + V _LED . The voltage +V _LED is generated in response to a current sense feedback signal (CSFB) 10 from one of the control ICs 6. The supply voltage varies with the number "m" of LEDs connected in series and can range from 35 volts for a string of 10 LEDs up to 150 volts for a string of 40 LEDs. Discrete protection devices 3A through 3Q (typically high voltage discrete MOSFETs) are used to clamp the maximum voltage present across the current slot transistor 4, particularly for operation at higher voltages (eg, above 100V).

In the system shown in Figure 1, the components are discrete devices in a single package, requiring only the pick and place operations of the components to position and mount them on their printed circuit boards.

For an "n" channel driver solution, each set of discrete components is repeated "n" times along with the corresponding LED string. For example, in addition to the SMPS 9, the 16-channel backlight system shown in Figure 1 requires 34 components (ie, microcontroller 7, a high-pin count backlight controller IC 6, 16 current-slot transistors 4 and 16). The protection device 3) facilitates regional dimming in response to video information generated by the scalar IC 8. This solution is both complicated and expensive.

In addition to the need to assemble a large number of discrete components (i.e., a high build-up material (BOM) number), the package cost of the high pin count package 6 is also considerable. The need for this large number of pins is shown in In the circuit diagram of FIG. 2, FIG. 2 illustrates a more detailed one of the channels of the LED driver system shown in FIG. 1. As shown, each channel includes a "m" series of LEDs 21 connected in series, one of the integrated high voltage circuit diodes 23, a protective MOSFET 22, a current sink MOSFET 24, and a current sense I. Precision gate driver circuit 25.

Active current tank MOSFET 24 implemented as a discrete component controlled by interface IC 6 includes a power MOSFET having a gate, source and drain connection, preferably a vertical DMOSFET. The I precision gate driver circuit 25 senses the current in the current tank MOSFET 24 and provides the necessary gate drive voltage for the sense current tank MOSFET 24 to conduct a precise amount of current. In normal operation, current sink MOSFET 24 operates in its saturation mode of operation to control a constant level independently of its drain to source voltage. Power is consumed in MOSFET 24 due to the simultaneous presence of a source-drain voltage and current. In order to detect shorted LEDs and facilitate feedback to the switched mode power supply (SMPS) 9, the drain voltage of the current sink MOSFET 24 needs to be continuously measured. The presence of a shorted LED is recorded in an LED fault circuit 27, and the feedback to the SMPS 9 is performed by a current sense feedback (CSFB) circuit 26.

In summary, the current-slot MOSFET 24 requires three connections to the control IC 6, in particular one of the source connections for current measurement, one for the biasing device to control the current of the device, and for One of the fault and feedback sensing is connected to the drain. These three connections per current-slot MOSFET (and thus each channel) are depicted in Figure 2A as spanning one interface 28 between the discrete device and a control IC. Even in the schematic circuit diagram of FIG. 2B, in which the spliced clamp MOSFET 22 and the current sink MOSFET 24 must be maintained at a high voltage (illustrated by the "HV" integrated body 23), each channel still needs to be traversed per channel. Three pins of interface 28. This requirement for 3 pins per channel explains the need for the high pin count package 6 shown in FIG. For a 16-channel driver, 48 pins per channel require 48 pins for controlling the output pins on the IC. Considering the SPI bus interface, analog function, power supply and more, an expensive 64 or 72 pin package is necessary. Worse, many TV prints The board assembly company was unable to solder the package with a pin pitch of slightly less than 0.8 mm or 1.27 mm. One of the 72 pin packages with a 0.8 mm pin pitch requires a 14 mm x 14 mm plastic body to provide the peripheral linear edge required to fit all the pins.

One significant problem with the multi-wafer system shown in Figure 1 is that the temperature sensed in interface IC 6 can only detect the temperature of the IC, with no significant power consumption occurring. Unfortunately, heat is generated in the discrete current sink DMOSFET 4, but temperature sensing is not possible. In the absence of zone temperature sensing, any of the current sink MOSFETs 4A through 4Q may overheat and the system may not detect or repair this state.

In summary, today's implementations of LED backlights for LCD panels with regional dimming capabilities are subject to numerous fundamental limitations regarding cost, performance, features, and security.

The highly integrated LED driver solution requires expensive, large-area dies that are packaged in expensive high-pin packages and concentrates heat in a single package. The driver is limited to lower currents due to power consumption caused by linear operation of the current-slot MOSFET, and power consumption due to LED forward voltage mismatch (one of the problems in a larger number of series-connected LEDs) The driver is limited to a lower voltage.

Multi-chip solutions that combine an LED controller with discrete power MOSFETs require high BOM counts and even higher pin count packages. With nearly three times the number of pins with fully integrated LED drivers, a 16-channel solution can require 33 to 49 components and a 14mm x 14mm 72-pin package. In addition, discrete MOSFETs do not have any thermal sensing or protection for overheating.

What is needed is a cost effective and reliable backlight system for a TV with regional dimming. This requires a new semiconductor chipset that eliminates discrete MOSFETs, provides lower overall package cost, minimizes thermal concentration within any component, facilitates overtemperature detection and thermal protection, protects low voltage components from high voltage and shorts LEDs The effect, elastic scaling to accommodate different numbers of channels and different sized displays without the need for custom integrated circuits, and to maintain precise control of LED current and brightness.

Ideally, an elastic solution can be sized to accommodate different numbers of channels and different sized display panels without the need for custom integrated circuits.

An LED driver system in accordance with the present invention meets the above criteria. An LED driver IC includes a function latch and a sequence of illumination interface (SLI) bus bars. The sequence illumination interface bus itself includes a first code register and a data register. The first code register is connected in series with the data register. The LED driver IC drives an external LED string.

Loading the data of the identification function latch into the first code register, and continuously loading data identifying a functional state of the LED driver IC into the data register (usually on a continuous clock pulse) . Responding to the data in the first code register, forming a connection between the function latch and the data register, and generally transmitting the data in the data register to the function latch when a synchronization pulse occurs .

In an embodiment, a plurality of LED driver ICs are configured to control one of a plurality of LED strings and one LED driver system. The SLI busbars in the respective LED driver ICs are connected in series to form a system SLI busbar. The data is continuously loaded into the system SLI bus such that the first code register and the data register in each LED driver IC contain the information needed to identify and control one of the function latches in the LED driver IC.

In a group embodiment, each LED driver IC further includes a preload latch and moves data from the data buffer to the function latch in two stages: first from the data register To the preload latch, and then from the preload latch to the function latch. The transfer of data from the preload latch to the function latch in all of the LED driver ICs can be performed simultaneously, so that the function latches in the various LED driver ICs are simultaneously updated. For example, this feature helps eliminate "flicker" when the LED string controlled by the LED driver IC is used in a flat panel display.

Each of the LED driver ICs can include a plurality of "channels", each channel being an external LED string and controlling one of the currents in the external LED string. Show. In addition, a plurality of functional latches can be associated with each of the channels, and the functional latches can be used to control, for example, the on-time of the current-slot MOSFET, the magnitude of the current in the current-slot MOSFET, and the current-slot MOSFET Associate one of the phase delays and define when the LED string associated with the channel experiences a fault condition.

In some embodiments, the LED driver IC includes one of a latch that holds data to be transferred to a data register in the SLI bus. The data in this latch can indicate the type of fault experienced by the LED string or driver IC, such as a shorted LED, a broken LED string, or an over temperature condition. After the data has been transferred to the data register in the SLI bus, the data is sent back to an external interface IC as the next data sequence is loaded into the SLI bus. The interface IC in combination with other components of the system (e.g., a microcontroller) can then take remedial action, such as disconnecting the LED string.

In some embodiments, the first code register is further divided into a channel first code register and a function first code register, the former saves data identifying one channel in the LED driver IC, and the latter saves and identifies the channel. A function of the function latch.

The SLI bus and LED driver ICs of the present invention are capable of high dimensional scaling and use semiconductor areas that are much smaller than prior art systems. For example, an 8-bit channel first code register, an 8-bit function first code register, and a 16-bit data register are theoretically available for 65,536 control bits in each of 256 channels. 256 function latches are controlled in principle, although a large number of such bits are not used in many embodiments.

1‧‧‧Multi-die LED driver system

2‧‧‧LED string

2A‧‧‧LED string

2B‧‧‧LED string

2C‧‧‧LED string

2D‧‧‧LED string

2E‧‧‧LED string

2F‧‧‧LED string

2G‧‧‧LED string

2H‧‧‧LED string

2I‧‧‧LED string

2J‧‧‧LED string

2K‧‧‧LED string

2L‧‧‧LED string

2M‧‧‧LED string

2N‧‧‧LED string

2P‧‧‧LED string

2Q‧‧‧LED string

3‧‧‧protection device

3A‧‧‧High voltage protection device

3B‧‧‧High voltage protection device

3C‧‧‧High voltage protection device

3D‧‧‧High voltage protection device

3E‧‧‧High voltage protection device

3F‧‧‧High voltage protection device

3G‧‧‧High voltage protection device

3H‧‧‧High voltage protection device

3I‧‧‧High voltage protection device

3J‧‧‧High voltage protection device

3K‧‧‧High voltage protection device

3L‧‧‧High voltage protection device

3M‧‧‧High voltage protection device

3N‧‧‧High voltage protection device

3P‧‧‧High voltage protection device

3Q‧‧‧High voltage protection device

4‧‧‧current slot transistor

4A‧‧‧current slot transistor

4B‧‧‧current slot transistor

4C‧‧‧current slot transistor

4D‧‧‧current slot transistor

4E‧‧‧current slot transistor

4F‧‧‧current slot transistor

4G‧‧‧current slot transistor

4H‧‧‧current slot transistor

4I‧‧‧current slot transistor

4J‧‧‧current slot transistor

4K‧‧‧current slot transistor

4L‧‧‧current slot transistor

4M‧‧‧current slot transistor

4N‧‧‧current slot transistor

4P‧‧‧current slot transistor

4Q‧‧‧current slot transistor

6‧‧‧Backlight controller integrated circuit

7‧‧‧Backlight Microcontroller

8‧‧‧ scalar integrated circuit

9‧‧‧Switch mode power supply

10‧‧‧ Current sensing feedback signal

11‧‧‧Common LED power supply rail

12‧‧‧Sequence Peripheral Interface (SPI) Busbars

21‧‧‧LED string

22‧‧‧Protect laminated MOSFETs

23‧‧‧Integrated high voltage circuit diode

24‧‧‧ Current Slot MOSFET

25‧‧‧ Current Sensing I Precision Gate Driver Circuit

26‧‧‧ Current sensing feedback circuit

27‧‧‧LED fault circuit

28‧‧‧ interface

50‧‧‧LED driver

51‧‧‧LED Driver IC

52A‧‧‧LED string

52B‧‧‧LED string

53‧‧‧Filter capacitor

54‧‧‧Iset resistor

55A‧‧‧ Current Slot DMOSFET

55B‧‧‧ Current Slot DMOSFET

56A‧‧‧I Precision Gate Driver Circuit / I Precision Circuit

56B‧‧‧I Precision Gate Driver Circuit / I Precision Circuit

57A‧‧‧Drawing clamped DMOSFET

57B‧‧‧Drawing clamped DMOSFET

58A‧‧‧Integrated high voltage diode/PN diode

58B‧‧‧Integrated high voltage diode/PN diode

59‧‧‧Digital control and sequential circuits

60‧‧‧ analog control and sensing circuit

61‧‧‧SLI (Sequence Lighting Interface) Bus Displacement Register

62‧‧‧Biasing Circuit / Bias Supply and Regulator

80‧‧‧LED driver

81‧‧‧LED Driver IC

81A‧‧‧LED Driver IC

81H‧‧‧LED Driver IC

82‧‧‧Iset resistor

83A‧‧‧LED string

83B‧‧‧LED string

83C‧‧‧LED string

83D‧‧‧LED string

83E‧‧‧LED string

83F‧‧‧LED string

83G‧‧‧LED string

83H‧‧‧LED string

83I‧‧‧LED string

83J‧‧‧LED string

83K‧‧‧LED string

83L‧‧‧LED string

83M‧‧‧LED string

83N‧‧‧LED string

83P‧‧‧LED string

83Q‧‧‧LED string

84‧‧‧Pressure supply and regulator/bias circuit

85‧‧‧ analog control and sensing circuit

85A‧‧‧ analog control and sensing circuit

85H‧‧‧ analog control and sensing circuit

86A‧‧‧I Precision Gate Driver Circuit

86B‧‧‧I Precision Gate Driver Circuit

86P‧‧‧I Precision Gate Driver Circuit

86Q‧‧‧I Precision Gate Driver Circuit

87A‧‧‧ Current Slot DMOSFET

87B‧‧‧ Current Slot DMOSFET

87P‧‧‧ Current Slot DMOSFET

87Q‧‧‧ Current Slot DMOSFET

88A‧‧‧Integrated HV diode

88B‧‧‧Integrated HV diode

88P‧‧‧Integrated HV diode

88Q‧‧‧Integrated HV diode

89‧‧‧Digital control and sequential circuits

89A‧‧‧Digital Control and Timing Circuit

89H‧‧‧Digital Control and Sequencing Circuit

90‧‧‧Sequence lighting interface bus

90A‧‧‧Sequence Lighting Interface Bus/SLI Bus Displacement Register

90H‧‧‧Sequence lighting interface bus

100‧‧‧Distributed multi-channel LED backlight driver system

101‧‧‧Intermediate area circuit (IC)

102‧‧‧ capacitor

107‧‧‧Common signal line

108‧‧‧Switch mode power supply

109‧‧‧ line

110‧‧‧Fixed +24V supply rail

111‧‧‧ Current feedback signal

112A‧‧‧CSFB line

112B‧‧‧CSFB line

112C‧‧‧CSFB line

112D‧‧‧CSFB line

112E‧‧‧CSFB line

112F‧‧‧CSFB line

112G‧‧‧CSFB line

112H‧‧‧CSFB line

112I‧‧‧CSFB line

113A‧‧‧ signal line

113B‧‧‧ signal line

113C‧‧‧ signal line

113D‧‧‧ signal line

113E‧‧‧ signal line

113F‧‧‧ signal line

113G‧‧‧ signal line

113H‧‧‧ signal line

113I‧‧‧ signal line

122‧‧‧Sequence peripheral interface bus

123‧‧‧Sequence illumination interface unit/sequence illumination interface busbar circuit

124‧‧‧Sequence and Control Unit

125‧‧‧Voltage Reference Source

126‧‧‧ bias supply unit

127‧‧‧Operation transconductance amplifier

152‧‧‧Host μC

153‧‧‧ scalar integrated circuit

204‧‧‧Resistors

210A‧‧‧Latch and counter A circuit

210B‧‧‧Latch and Counter B Circuit

211A‧‧‧D latch

211B‧‧‧D latch

212A‧‧‧Φ latch

212B‧‧‧Φ latch

213A‧‧D/A converter

213B‧‧D/A converter

214‧‧‧Fault latch circuit

215‧‧‧LED fault detection circuit

216‧‧‧ Temperature detection circuit

217‧‧‧Reference current source

218‧‧‧ Current sensing feedback circuit

219‧‧‧MOSFET

220A‧‧‧PWM A register

220B‧‧‧PWM B register

221A‧‧‧ Phase A register

221B‧‧‧ Phase B register

222A‧‧‧Spot A register

222B‧‧‧like point B register

224‧‧‧Fault setting register

225‧‧‧ Fault Status Register

250‧‧‧LED Driver System

251A‧‧‧LED Driver IC

251B‧‧‧LED Driver IC

251C‧‧‧LED Driver IC

251D‧‧‧LED Driver IC

251E‧‧‧LED Driver IC

251F‧‧‧LED Driver IC

251G‧‧‧LED Driver IC

251H‧‧‧LED Driver IC

252‧‧‧Interface IC

253‧‧‧ data sequence

301‧‧‧LED Driver IC

302‧‧‧ Current setting resistor

303A‧‧‧LED string

303B‧‧‧LED string

303C‧‧‧LED string

303D‧‧‧LED string

304‧‧‧ bias supply

306A‧‧‧I Precision Gate Driver Circuit

306B‧‧‧I Precision Gate Driver Circuit

306C‧‧‧I Precision Gate Driver Circuit

306D‧‧‧I Precision Gate Driver Circuit

307A‧‧‧ Current Slot DMOSFET

307B‧‧‧ Current Slot DMOSFET

307C‧‧‧ Current Slot DMOSFET

307D‧‧‧ Current Slot DMOSFET

308A‧‧‧High Voltage Diode

308B‧‧‧High Voltage Diode

308C‧‧‧High Voltage Diode

308D‧‧‧High Voltage Diode

309‧‧‧Digital control and sequential circuits

310‧‧‧ analog control and sensing circuit

311‧‧‧SLI busbar displacement register

312‧‧‧first code register

312C‧‧‧First Code Scratchpad/Channel First Code Scratchpad

312F‧‧‧first code register/function first code register

313‧‧‧data register

354‧‧‧ Fault Status Register

355‧‧‧ Fault Status Register

402‧‧‧Digital Control and Sequential Circuits

403‧‧‧ analog control and sensing current

410‧‧‧SLI busbar

410A‧‧‧Latch and counter A circuit

410B‧‧‧Latch and Counter B Circuit

411A‧‧‧D latch

411B‧‧‧D latch

412A‧‧‧Φ latch

412B‧‧‧Φ latch

413A‧‧D/A converter

413B‧‧D/A converter

414‧‧‧Fault latch circuit

419‧‧‧first code decoder and multiplexer circuit

451‧‧‧first code decoder

452‧‧‧ function selection output

453‧‧‧Channel selection output

454‧‧‧Multiplexer Circuit

455‧‧‧Latch

456‧‧‧ analog or digital function

457‧‧‧ channel

491‧‧‧Decoder

492‧‧‧Multiplexer

501‧‧‧4-channel LED driver IC

503A‧‧‧LED string

503B‧‧‧LED string

503C‧‧‧LED string

503D‧‧‧LED string

506A‧‧‧I Precision Gate Driver Circuit

506B‧‧‧I Precision Gate Driver Circuit

506C‧‧‧I Precision Gate Driver Circuit

506D‧‧‧I Precision Gate Driver Circuit

507A‧‧‧ Current Slot DMOSFET

507B‧‧‧ Current Slot DMOSFET

507C‧‧‧ Current Slot DMOSFET

507D‧‧‧ Current Slot DMOSFET

509‧‧‧Digital control and sequential circuits

510‧‧‧ analog control and sensing circuit

511‧‧‧Multiplexer

512‧‧‧SLI Bus Displacement Register/SLI Bus Interface

513‧‧‧Decoder

531‧‧‧LED Driver IC

539‧‧‧Digital control and sequential circuits

540‧‧‧ analog control and sensing circuit

541‧‧‧Double-channel multiplexer

542A‧‧‧SLI busbar displacement register

542B‧‧‧SLI Bus Displacement Register

543A‧‧‧Decoder

543B‧‧‧Decoder

601‧‧‧Decoder

602C‧‧‧ magnitude comparator

602F‧‧‧ magnitude comparator

603‧‧‧Digital Logic Gate

604‧‧‧Multiplexer

605C‧‧‧Decoding key/channel selection code key

605F‧‧‧Decode/Function Code Key

606‧‧‧ function latch

607‧‧‧Function Latch Library

611‧‧‧Decoder

612C‧‧‧ magnitude comparator

612F‧‧‧ magnitude comparator

613‧‧‧AND gate

614‧‧‧Multiplexer

615C‧‧‧ register

615F‧‧‧ register

616‧‧‧ function latch

621‧‧‧Decoder

622C‧‧‧Quantity Comparator

622F‧‧‧ magnitude comparator

623‧‧‧AND gate

624‧‧‧Multiplexer

625C‧‧‧ register

625F‧‧‧ register

626‧‧‧ function latch

626A‧‧‧ function latch

626B‧‧‧ function latch

631‧‧‧Value comparator

632‧‧‧NOR gate/XNOR gate

633‧‧‧NOR gate/XNOR gate

634‧‧‧NOR gate

635‧‧‧AND gate

636‧‧‧channel or function code key

637‧‧‧Multi-channel magnitude comparator gate

641A‧‧‧ magnitude comparator

641B‧‧‧Value comparator

641D‧‧‧ magnitude comparator

642A‧‧‧Value comparator

642B‧‧‧ magnitude comparator

642H‧‧‧ magnitude comparator

643A1‧‧‧Logical AND gate

643B1‧‧‧Logical AND gate

643A2‧‧‧Logical AND gate

643D8‧‧‧Logical AND gate

644A‧‧‧Inverter

644B‧‧‧Inverter

645A‧‧‧P channel MOSFET

645L‧‧‧P channel MOSFET

646A‧‧‧P channel MOSFET

646H‧‧‧P channel MOSFET

647‧‧‧Decoded channel bus/four channel bus

648‧‧‧Decoded function bus/eight function bus

649‧‧‧ data bus

655‧‧‧Preloaded latches

656‧‧‧Active function latch

657‧‧‧Control function

701A‧‧‧LED Driver IC

701B‧‧‧LED Driver IC

701C‧‧‧LED Driver IC

701D‧‧‧LED Driver IC

701E‧‧‧LED Driver IC

701F‧‧‧LED Driver IC

701G‧‧‧LED Driver IC

701H‧‧‧LED Driver IC

771‧‧‧Sequence clock SCK signal

773‧‧‧Preloaded latches

774‧‧‧ Duration

801‧‧‧Timed Waveform/SCK Pulse

802‧‧‧Timed Waveform/Vsync Pulse

803A‧‧‧SCK Crowd

803B‧‧‧SCK Crowd

803C‧‧‧SCK Crowd

803D‧‧‧SCK bursts

803E‧‧‧SCK Crowd

803F‧‧‧SCK

803G‧‧‧SCK bursts

803H‧‧‧SCK bursts

851‧‧‧ data sequence

852‧‧‧ data sequence

891‧‧‧Broadcast sequence

b ₁ , b ₈ , b ₁₂ ‧ ‧ bus bar

CSFBI‧‧‧ input pin

CSFBO‧‧‧ output pin

D _B ‧‧‧Information

D _D ‧‧‧Information

D _F ‧‧‧Information

D _H ‧‧‧Information

D _J ‧‧‧Information

D _L ‧‧‧Information

D _N ‧‧‧Information

D _Q ‧‧‧Information

FLT‧‧‧Digital Fault Line/Fault Interrupt Line

GSC‧‧‧ Grayscale Clock

SC‧‧‧Sequence Clock

SCK‧‧‧Digital Clock/Sequence Clock

SI‧‧‧Sequence input

SO‧‧‧Sequence output

t _latch ‧ ‧ duration

Vcc‧‧‧ power supply

Vref‧‧‧reference voltage

Vsync‧‧‧ digit clock/pulse

1 illustrates a diagram of a prior art multi-channel LED drive system for a LCD backlight using discrete DMOSFETs as integrated current sinks and protection voltage clamps.

2A is a schematic circuit diagram of an individual LED drive channel using one discrete DMOSFET as one of the current slots of a DMOSFET with a protection high voltage splicing clamp.

2B is a schematic circuit diagram of a discrete high voltage DMOSFET as one of the individual LED drive channels without one of the stacking current slots.

Figure 3A is a schematic circuit diagram of a dual channel high voltage smart LED driver with serial bus control and a protection high voltage spliced clamp DMOSFET.

Figure 3B is a schematic circuit diagram of a dual-channel high-voltage smart LED driver with serial bus control and a high-voltage current-slot MOSFET without a stacked clamp MOSFET.

4 is a schematic circuit diagram of a multi-channel LED backlight system including a smart LED driver having a current sense feedback (CSFB) system and an SLI sequence bus.

Figure 5 is a simplified schematic diagram of one of the systems shown in Figure 4, showing a significantly reduced construction material (BOM) that can be achieved using smart LED drivers with SLI sequence bus control and a low pin count interface IC package. ).

Figure 6 is a block diagram of a "complex" SLI bus register with a corresponding digital control and timing (DC&T) and analog control and sensing (AC&S) in a dual channel smart LED driver.

Figure 7 is a timing diagram of one of the SLI bus bars controlling a plurality of LED drivers.

Figure 8 is a schematic circuit diagram of one of four-channel high-voltage smart LED drivers with an SLI bus and high voltage current-slot MOSFET and no stacked clamp MOSFET.

Figure 9 is a diagram of one of the "complex" SLI busbars of a four-channel LED driver IC.

FIG. 10 is a block diagram showing a dual-channel smart LED driver having a corresponding digital control and timing (DC&T) and analog control and sensing (AC&S) one of the first code multiplexed SLI bus registers.

Figure 11 is a block diagram of one of the first code multiplexed SLI bus bars including channel and function decoding.

Figure 12A is a schematic circuit diagram of one of the dual-channel high voltage smart LED drivers with first code multiplexed SLI bus control and a single multiplexer.

Figure 12B is a first code multiplex SLI bus control and a single multiplexer One of the high-voltage smart LED drivers is a schematic circuit diagram.

Figure 12C is a schematic circuit diagram of one of the four-channel high voltage smart LED drivers with first code multiplexed SLI bus control and one dual multiplexer.

Figure 13A shows an embodiment of a LED driver IC including a 4-channel 8-function SLI bus decoder and a multiplexer.

Figure 13B shows an embodiment of a LED driver IC including a 4-channel 4-function SLI bus decoder and a multiplexer.

Figure 13C shows an embodiment of a LED driver IC including a 2-channel 4-function SLI bus decoder and a multiplexer.

Figure 13D shows an example of a magnitude comparator.

Figure 13E shows an example of a function and channel decoder using an AND gate and a multiplexer.

14 is a block diagram showing one of the three-level register-latch architectures including a pre-loaded latch and an active latch, a first-code multiplexed SLI bus register.

Figure 15 illustrates an SLI bus data sequence including one of the six channel driver ICs having four independent functions.

Figure 16A shows a flow diagram of an initialization and scratchpad update algorithm for an SLI bus with one of a plurality of function registers.

Figure 16B is a flow chart showing one of the procedures for synchronously writing to a plurality of preload latches.

Figure 16C shows a data sequence of one of the 16 channel 4 functional systems with one of the eight LED driver ICs.

Figure 17A illustrates a sequence of data for updating only one of the PWM latches in a 16 channel system.

Figure 17B illustrates a sequence of data for selectively updating a channel using a "casual" first code state.

17C illustrates channels, functions, and arbitrary commands in a single SLI bus broadcast. A mix of one data sequence.

As described in the background paragraph, existing backlight solutions for TV and large screen LCDs are complex, expensive, and inelastic. To reduce the cost of backlighting systems with regional dimming LCDs without sacrificing safety and reliable operation, a new architecture is needed that eliminates at least discrete MOSFETs, minimizes thermal concentration within any component, facilitates overtemperature detection, and thermal protection. Protect low voltage components from high voltages. While meeting these objectives may not be sufficient to achieve a cost-effective solution that meets one of the cost targets of the home electronics market, this improvement is one of the goals of achieving low-cost regional dimming. The first step is necessary.

The invention described herein enables a new cost effective and scalable architecture to enable safe and economically viable LED backlighting solutions for large screen LCDs and TVs with energy efficient regional dimming capabilities. This new LED driver system, feature distribution and architecture overcomes these cost, functional issues and the need for high pin count packages. The new architecture is based on some basic premises, including:

1. The analog control, sensing and protection of the current-slot MOSFET should be functionally integrated with the current-slot MOSFET itself in the same IC rather than being separated into another IC.

2. Basic dimming, phase delay, LED current control, and channel-specific functions should be functionally integrated with the current-slot MOSFET in the same IC rather than being separated into another IC.

3. System timing, system μC host negotiation, and other global parameters and functions not unique to a particular channel should not be functionally integrated with the current slot MOSFET in the same IC.

4. The number of channels (ie, current-slot MOSFETs) in a device package should be designed for thermal management (ie, avoiding overheating) while meeting specified LED current, supply voltage, and LED forward voltage mismatch requirements.

5. The communication and control of the multi-channel LED driver IC should be packaged in a low pin count. Ideally, no more than three package pins are required on the central interface IC and each driver IC. The communication circuit should occupy only a small portion of the die area and cost of the driver IC.

6. The functional integration of the interface IC and LED driver IC should be balanced to facilitate the use of low cost and low pin count packages that are compatible with a single layer PCB assembly.

7. Ideally, the system should be flexibly scaled to any number of channels without the need for significant redesign of such ICs.

The conventional architecture of Figure 1 (i.e., a centralized controller that drives several discrete power MOSFETs) fails to meet even one of the above objectives, primarily because it requires control of a central point or "command center" for All digital and analog information processing. Necessarily, the command center IC must communicate with its μC master and directly sense and drive each current sink MOSFET. This high component connectivity requires a large number of input and output lines, making high pin count packages necessary.

Decentralized LED Driver Architecture Overview

The solution to the problem of prior art systems is a "decentralized" system, lacking a centrally controlled, decentralized system. In the decentralized system described herein, an interface IC translates information obtained from the host μC into a simple sequence communication protocol that digitally routes instructions to any number of "smart" satellite LED drivers on a sequence of busses. IC. An embodiment of an LED driver that satisfies one of the above criteria is described in the above-cited application Serial No. 13/346,625. For the sake of brevity, the main concepts of this application, which are related to the subject matter of this application, are repeated in this document, including the description of the interface and LED driver IC, and the "Sequence Lighting Interface" (or SLI) bus (including and controlling LED lighting). The operation of one of the specific related parameters is agreed.

In a preferred embodiment, the SLI sink eliminates the control of the LED driver and also returns to the interface IC in a "daisy chain" connection, causing a fault condition (such as an open circuit) to occur in any of the driver ICs. The LED, a shorted LED or an overtemperature fault can be communicated back to the interface IC and ultimately to the host μC. Each driver IC responds to its SLI Bus digital instructions, with the help of interface ICs, perform all necessary LED driver functions, such as dynamic precision LED current control, PWM brightness control, phase delay and fault detection.

Each LED driver IC also includes input and output pins for a similar current sense feedback (CSFB) signal. The CSFB line connects the LED driver IC to the interface IC to form a second daisy chain to allow the interface IC to provide a feedback signal to a high voltage switched mode power supply (SMPS) that dynamically regulates the voltage supplied to the LED string. Under this architecture, a dual channel LED driver IC can be easily adapted to a standard SOP 16 package or any similar lead package.

In addition to the SPI bus-to-SLI bus translation responsibility of the interface IC, the interface IC also supplies a reference voltage to all LED driver ICs required to ensure good current matching, generating Vsync and gray-scale clock GSC pulses to synchronize their operation. And monitor for possible failures of each LED driver IC. It also facilitates voltage-to-current translation of the CSFB signal to the ICSFB signal using an on-wafer transconductance amplifier or OTA. Even with all of the above features, the interface IC can be easily adapted to an SOP 16 package.

This application describes an improved sequence communication protocol and method of reducing the size of circuitry associated with the physical interface of the SLI bus. These improvements are expressly expressed in the heading "Improved SLI Bus Interfaces and Agreements" below. However, in the beginning, useful descriptions describe the basic architecture of LED drivers controlled by serial bus, video system interface ICs, and the first generation of "complex" SLI bus protocol.

LED driver with integrated dimming and fault detection

One embodiment of an LED driver 50 in accordance with the present invention formed in an LED driver IC 51 is shown in FIG. 3A. The LED driver 50 integrated in an LED driver IC 51 is a dual channel driver including integrated current tank DMOSFETs 55A and 55B, and stacked clamped DMOSFETs 57A and 57B having integrated high voltage diodes 58A and 58B for Accurate current controlled I precision gate driver circuits 56A and 56B, analog control and sense The circuit 60 and a digital control and timing circuit 59 are provided. A chip bias supply and regulator 62 supplies power to the IC.

One of the channels includes a current sink DMOSFET 55A, a stacked clamp DMOSFET 57A, and an I precision gate driver circuit 56A that together drive an LED string 52A. The other channel includes a current sink DMOSFET 55B, a stacked clamp DMOSFET 57B, and an I precision gate driver circuit 56B that together drive an LED string 52B.

LED driver 50 provides full control of two channels of 250mA LED drive with 150V circuit capability and ±2% absolute current accuracy, 12-bit PWM brightness control, 12-bit PWM phase control, 8-bit current control , LED open and short-circuit fault detection and over-temperature detection, all controlled by a high-speed sequential illumination interface (SLI) bus displacement register 61, and using a common Vsync and gray-scale clock (GSC) Signals are synchronized to other drives. In one embodiment, the stacked clamp DMOSFETs 57A and 57B have a nominal circuit capability of 150V, although in other embodiments, such devices can be sized to operate in the range of 100V to 300V. The rated current of 250 mA is set by the power consumption of the package and the mismatch of the forward voltages in the two LED strings 52A and 52B.

In operation, LED driver 50 receives a data stream on its serial input SI pin that is fed into the input of SLI bus bar register register 61. The data is clocked at a rate set by one of the sequence clock signals SCK supplied by the interface IC (not shown in Figure 3A). The maximum clock rate for this data depends on the CMOS technology used to implement the shift register 61, but even with a 0.5 μm line width program and fab, a 10 MHz operation can be achieved. As long as the SCK signal continues to run, the data will be moved to the SLI bus shift register 61 and eventually exit the sequence output pin SO on its path to the next LED driver (not shown in Figure 3A) in the sequence daisy chain. .

After the data corresponding to the particular LED driver IC reaches the SLI bus shift register 61, the interface IC stops transmitting the SCK signal. Subsequently, a Vsync pulse latches the data from the SLI bus shift register 61 into the digital control and sequential circuitry. In the data latches of 59 and analog control and sense circuit 60, the latches typically include a flip-flop or a static RAM. Also at this Vsync pulse, any data previously written to the fault latch contained in the analog control and sense circuit 60 will be copied into the appropriate bits of the SLI bus shift register 61.

When the interface IC resumes transmitting the sequence clock SCK signal, the read and write bits stored in the SLI bus shift register 61 are moved to the lower driver IC in the daisy chain. In a preferred embodiment, the daisy chain forms a connection back to one of the loops of the interface IC. Sending new data to the daisy chain ultimately pushes existing data residing in the SLI busbar shift register through the loop and ultimately back to the interface IC. In this manner, the interface IC can communicate with individual LED driver ICs, set LED string brightness and timing, and the individual LED driver ICs can communicate individual fault conditions back to the interface IC.

Using this timing scheme, the data can be shifted through a large number of driver ICs at high speed without affecting the LED current or causing flicker, since the current and timing of the control current tank DMOSFETs 55A and 55B are only changed when each new Vsync pulse occurs. Vsync can be scaled proportionally to the grayscale clock frequency (typically 4096 times the Vsync frequency) and varied from 60 Hz to 960 Hz. Since Vsync is slower (less than 1 kHz), the interface IC can perform additional functions (if needed) to, for example, modify and resend the data when compared to the frequency of the SCK signal that drives the SLI busbar shift register. , or query the fault latch multiple times for the duration of a given Vsync pulse.

Starting at the Vsync pulse, the digital control and timing circuit 59 generates two PWM pulses to switch the output of the I precision gate driver circuits 56A and 56B to be turned on after the appropriate phase delay and the appropriate pulse width duration (or duration of action factor D). And closed. I precision gate driver circuits 56A and 56B sense the currents in current sink DMOSFETs 55A and 55B, respectively, and provide appropriate gate drive voltages for PWM pulses from digital control and timing circuit 59 at I precision gate driver circuits 56A and 56B. A target current is maintained during the time period of activation. The operation of I precision gate driver circuits 56A and 56B is thus similar to a "strobe" amplifier The operation is performed by turning on and off the digital pulse but providing a control function.

The peak current is globally set across all LED drivers by the Vref signal and by the value of the Iset resistor 54. In a preferred embodiment, the Vref signal is generated by the interface IC. Alternatively, the Vref signal can be supplied by a discrete voltage reference IC or as an auxiliary output from an AC/DC converter module.

The specific current in any of the LED strings can be further adjusted by adjusting the current of the current sink DMOSFET to one of the range of 0% to 100% of the peak current value. The 8 to 12-bit block is received by the SLI bus register. Controlled by the dot (Dot) register. In this way, the LED current can be accurately digitally controlled using this architecture, emulating a current mode digital to analog converter or "current DAC" function. In LCD backlight applications, this feature can be used to calibrate backlight brightness, to improve backlight uniformity, or for operation in 3D mode. In other cases, the LED drivers can be used to drive LED strings in a sign and "LED wall" displays (generally including a mix of red, green, and blue LEDs). In signage applications, the LEDs form an image such that an LCD is not required.

Referring to Figure 3A, the current flowing through LED string 52A is controlled by current sink DMOSFET 55A and corresponding I precision gate driver circuit 56A. Similarly, the current flowing through LED string 52B is controlled by current sink DMOSFET 55B and corresponding I precision gate driver circuit 56B. The maximum voltages applied to the current sink DMOSFETs 55A and 55B are limited by the stacked clamp DMOSFETs 57A and 57B, respectively. As long as the number of LEDs "m" is not too large, the voltage +V _LED will not exceed the breakdown voltage of the PN diodes 58A and 58B, and the maximum voltage on the current sink DMOSFETs 55A and 55B will be limited to about 10V, below One threshold voltage of the gate bias (12V in this embodiment) is applied to the stacked clamp DMOSFETs 57A and 57B by the bias circuit 62. Bias circuit 62 also generates a 5V supply voltage from the 24V VIN input to operate its internal circuitry using a linear voltage regulator and a filter capacitor 53.

The drain voltage on current sink DMOSFETs 55A and 55B is also controlled by analogy The measurement circuit 60 monitors and compares one of the overvoltage values stored in one of the latches in the analog control and sense circuit 60. This overvoltage value is supplied by the SLI bus displacement register 61. If the drain voltages of current sink DMOSFETs 55A and 55B are below the programmed value, LED strings 52A and 52B operate normally. However, if the drain voltage of the current sink DMOSFET 55A or the current sink DMOSFET 55B rises to about a programmed value, one or more of the LED strings 52A and 52B are shorted, and one of the specific channels is detected and recorded. Similarly, if the I precision gate driver circuit 56A or the I precision gate driver circuit 56B is unable to maintain the desired current in one of the LED strings 52A or 52B (i.e., the LED string operates under "out of current") This means that one of the LEDs in one of the strings 52A or 52B is not turned on and loses circuit continuity. Then close the corresponding channel, ignore the CSFB signal of the corresponding channel, and report the fault. Sensing "under current" can be performed by monitoring the saturation of the output of the gate buffer device in I precision circuits 56A and 56B. This state means that the buffer is driving the gate of the corresponding current sink DMOSFET as much as possible to "completely turn on". Alternatively, an undercurrent condition can be detected by monitoring the voltage drop across the input terminals of the I precision circuit. When the input voltage drop to I precision circuits 56A and 56B is too low, an undercurrent condition occurs and an open LED fault is indicated.

If an over-temperature condition is detected, the fault is reported and the channel remains on and conducted unless the interface IC sends a command to close the channel. However, if the temperature continues to rise to a dangerous level, the analog control and sensing circuit 60 will independently deactivate the channel and report the fault. Regardless of the nature of a fault (a shorted LED, a broken LED, or an overtemperature condition), as soon as a fault occurs, an open buck MOSFET in the analog control and sense circuit 60 will activate the FLT pin and pull the FLT pin At the low level, a situation in which a fault condition has occurred is signaled to the interface IC and signaled to the host μC as appropriate. The FLT pin informs the system IC of a system interrupt signal when a fault occurs in one or more of the LED driver ICs. Typically, the line is held at a high level, that is, biased to Vcc through a high value resistor. Any LED driver experiences a fault condition (a shorted LED, a broken LED or an over temperature) In either state, the particular LED driver IC pulls the line to a low level by enabling a grounded N-channel MOSFET (such as MOSFET 219 in Figure 6).

After the FLT is pulled to the low level, the interface IC can query the LED driver IC through the SLI bus interface 61 to determine which LED driver IC is experiencing a fault condition and what has occurred. The interface IC then communicates this message back to the host microcontroller via the SPI bus interface, allowing the system to make a decision as to what action, if any, should be taken in response to the failure. Since the FLT line on each LED driver IC uses an open MOSFET to actively pull the line to a low level when a fault occurs, the high value internal resistor will be used in the absence of a fault. Pull the line to a high level. Thus, the FLT input to the interface IC 101 of FIG. 4 can be connected in parallel with the interrupt input pin of the system μC, in which case any fault generated by the LED driver IC not only informs the interface IC 101 of a fault condition, but also An interrupt signal is generated in μC, and the state is warned to the μC. Thus, the FLT line is used to provide an immediate indication of one of the failures in an LED driver IC, while the SLI bus and SPI bus are used to collect additional information before deciding what action to take. In this way, full fault management can be performed without a fully integrated driver IC.

The analog control and sense circuit 60 also includes an analog current sense feedback (CSFB) signal equal to the lowest voltage of the drain voltages of the two current sink DMOSFETs 55A and 55B and the voltage at the CSFBI input pin. The CSFB signal is passed to the CSFBO output pin. In this manner, the lowest current slot voltage in LED strings 52A and 52B is passed to the input of the next LED driver and ultimately back to system SMPS to power the +V _LED supply rail.

In the manner described, an LED driver 50 with integrated dimming and fault detection capabilities is implemented without the need for a central controller IC.

An alternate embodiment of LED driver 80 that satisfies one of the above criteria is shown in FIG. 3B. The LED driver 80 integrated in an LED driver IC 81 is a dual channel driver having integrated current slot DMOSFETs 87A and 87B but without a stacked clamp MOSFET. Alternatively, DMOSFETs 87A and 87B include integrated high voltage diodes 88A and 88B that are designed to maintain a high voltage when DMOSFETs 87A and 87B are in a closed state. Typically, this design is best suited for operations below 100V, but can be extended to 150V if desired. As in the LED driver IC 50 of FIG. 3A, the I precision gate driver circuits 86A and 86B facilitate accurate current control controlled by an analog control and sense circuit 85 and a digital control and timing circuit 89. In this case, a on-wafer bias supply and regulator 84 is powered from Vcc rather than from the 24V input to the LED driver IC 81 as in the driver IC 51. In addition to the lack of a stacked clamp DMOSFET, the driver IC 80 operates similar to the driver IC 50, controlled through its SLI bus bar 90.

SLI bus interface IC and system application

4 illustrates a decentralized multi-channel LED backlight driver system 100 in accordance with the present invention. An interface IC 101 for driving a series of LED driver ICs 81A through 81H powered by a common switched mode power supply (SMPS) 108 is shown. Although only the LED driver ICs 81A and 81H are shown in FIG. 4, it should be understood that similar driver ICs 81B to 81G are located between the driver ICs 81A and 81H. Each of the LED driver ICs 81A through 81H has integrated dimming and fault detection capabilities, and is similar to the LED driver 80 shown in Figure 3B. LED driver ICs 81A through 81H are sometimes referred to herein collectively as LED driver ICs 81 or individually as LED driver ICs 81.

Five common signal lines 107 including three digital clock lines (SCK, GSC, and Vsync), one digital fault line (FLT), and one analog reference voltage line (Vref) are connected to the interface IC 101 and the LED driver ICs 81A to 81H. A timing and control unit 124 simultaneously generates Vsync and GSC signals from data received from a host μC (not shown) via a serial peripheral interface (SPI) bus 122. The timing and control unit 124 also monitors the fault interrupt line FLT to instantly detect one of the LED strings 81A through 81Q. A voltage reference source 125 provides a voltage reference across the Vref line to the system to ensure good channel-to-channel current matching. A bias supply unit 126 is fixed to +24V by being connected to one of the SMPS 108 supplies. The interface IC 101 is powered by supplying one of the VIN lines of the rail 110. Bias circuit 126 also produces a regulated supply Vcc (preferably 5V) to power LED driver ICs 81A through 81H. The Vcc supply is filtered by a capacitor 102.

In this embodiment, each of the LED driver ICs 81A through 81H includes two channels of high voltage current control, including current sink DMOSFETs 87A through 87Q with integrated HV diodes 88A through 88Q, and an accurate gate driver circuit. 86A to 86Q, digital control and timing (DC&T) circuits 89A through 89H, analog control and sense (AC&S) circuits 85A through 85H, and sequential illumination interface (SLI) bus bars 90A through 90H. As shown in Figure 3B, LED driver ICs 81 lack a stack of clamps. However, system 100 can also be fabricated with an LED driver IC similar to LED driver IC 51 shown in Figure 3A, except that in this case, 24V VIN supply, rather than Vcc, will be used to power and bias the LED driver ICs. Clamp the gate of the DMOSFET.

The SLI bus bar 113, which includes one of the signal lines 113A to 113I, connects the LED driver ICs 81A to 81H together into a daisy chain. In the embodiment shown in FIG. 4, the serial output terminal of the SLI unit 123 (the SO pin of the interface IC 101) is connected to the SI input of the LED driver IC 81A via a signal line 113A, and the SO output of the LED driver IC 81A. It is connected to the SI input of the LED driver IC 81B (not shown) via a signal line 113B, and so on. At the end of the daisy chain, the SO output of the LED driver IC 81H is connected to the serial input terminal of the SLI unit 123 (the SI pin of the interface IC 101) via a signal line 113I. In this manner, the SLI bus bar 113 forms a complete loop: originating from the interface IC 101, running through each of the LED driver ICs 81A through 81H, and returning to the interface IC 101. Therefore, the data is removed from the SO pin of the interface IC 101 while a string of equal lengths is transmitted back to the SI pin of the interface IC 101.

The SLI circuit 123 also generates an SLI bus timing signal SCK, if desired. Since the LED driver ICs 81A through 81H do not have an address, the number of bits through the SLI bus timing must correspond to the number of devices being driven, with each SCK pulse advancing by one bit. Be The number of devices driven can be adjusted by software exchange in the software-programmed SPI bus 122 or by hardware modification of the interface IC 101. In this manner, the number of channels within system 100 can be flexibly altered to match the size of the display.

Modifying the scratchpad in the SLI bus circuit 123 to remove fewer or more bits, while relatively simple, requires a modification in the fabrication of the interface IC 101. An alternative approach involves the use of a programmable interface that uses a software adjustment driver to accommodate fewer or more LED driver ICs in the daisy chain.

Current sensing feedback to SMPS 108 relies on a daisy chain. The CSFBI input pin of the LED driver IC 81H is connected to Vcc via the CSFB line 112I, the CSFBO output pin of the LED driver IC 81H is connected to the CSFBI input pin of the LED driver IC 81G, and so on. Finally, CSFB line 112A connects the CSFBO output pin of LED driver IC 81A to the CSFBI input pin of interface IC 101. The voltage level of the CSFB signal is decreased by driving one of the LED driver ICs 81A to 81H of an associated LED string 83A to 83Q having an LED driver that has previously passed the CSFB signal. The associated LED string has a higher forward voltage Vf. Since the LED driver ICs 81A to 81H are configured in a daisy chain, the CSFB signal is gradually reduced as it is transferred from the LED driver IC 81H to the LED driver IC 81A. The CSFB signal in the last CSFB line 112A represents the forward voltage Vf of the LED strings 83A to 83Q having the highest Vf throughout the LED array. The operational transconductance amplifier (QTA) 127 converts the CSFB signal in the CSFB line 112A into a current feedback signal ICSFB 111 that drives the voltage on the line 109 at the output of the SMPS 108 +V _LED for flicker free illumination without excessive power consumption. The best voltage. CSFB lines 112A through 112I are sometimes referred to herein collectively as CSFB lines 112.

The resulting system shown in the simplified schematic of Figure 5 uses only eight small LED driver ICs 81A through 81H to achieve independent control and constant current drive of 16 LED strings 83A through 83Q, all of which are responsive to A host μC 152 and a scalar IC 153 are controlled by the interface IC 101 through the SLI bus bar 113 (including the signal lines 113A to 113I). Only two analog signals are presented in the system: one common reference voltage Vref on line 107 and the ICSFB signal 111 that controls SMPS 108 to produce a +V _LED output on line 109. As described above, the ICSFB signal 111 is generated in the interface IC 101 by the CSFB signals on lines 112A through 112H. In the case of discrete analog DMOSFETs with less analog signals and no high impedance inputs, the LED driver system 100 also has relatively high noise immunity.

As shown in FIG. 5, LED driver system 100 can be fabricated using only nine SOP 16 IC packages (one interface IC and eight LED driver ICs) to drive 16 LED strings. Compared to the multi-wafer LED driver system of Figure 1, which uses 32 discrete MOSFETs and a 72-pin controller IC, this new architecture significantly reduces manufacturing costs. System reliability is also enhanced by significantly fewer components. System 100 is also easy to deploy because only the dedicated SLI bus protocol is used between interface IC 101 and satellite LED driver ICs 81A through 81H. The μC 152 communicates with the interface IC 101 and the scalar IC 153 via an SPI bus.

The LED driver ICs 81A through 81H of Figure 5 require only a 5V Vcc input without a stacked clamp DMOSFET. Therefore, the interface IC 101 can perform 24V to 5V voltage conversion and distribute its 5V supply rail Vcc to the LED driver ICs 81A to 81H. By eliminating the need for buck regulation in the LED driver ICs 81A through 81H, the LED driver ICs 81A through 81H can be made smaller and eliminate the need for an external filter capacitor, saving one package pin.

"complex" SLI bus operation

To eliminate the need for high pin count packages, we have disclosed herein a new serial communication bus and protocol specifically designed to drive LEDs in backlighting and display applications. The "Sequence Lighting Interface" bus or SLI bus uses a one-sequence communication method that includes one of a sequence of input and output timing shift registers and a timing and rate of control data transfer.

The operation of the SLI bus bar is illustrated in Figure 6, which also provides the SLI sink shown in Figure 4. More details of the construction and operation of the exemplary embodiment of the stream displacement register 90A, the digital control and timing (DC&T) circuit 89A, and the analog control and sense (AC&S) circuit 85A. It should be understood that similar circuits are used for the SLI busbar shift registers 90B through 90H, the digital control and timing circuits 89B through 89H, and the analog control and sense circuits 85B through 85H shown in FIG. (SLI busbar shift registers 90A through 90H are sometimes collectively referred to as SLI bus bars 90). 6 shows a dual channel LED driver IC including current sink DMOSFETs 87A and 87B and I precision gate driver circuits 86A and 86B, but LED driver ICs that control a different number of channels can be implemented in a similar manner.

The circuit shown in Figure 6 is a mixed signal combining both digital signals and analog signals. The SLI bus displacement register 90A is connected to the DC&T circuit 89A by a number of parallel data busses (typically 12-bit wide), and is also within the range of 4 bits wide to 12 bits wide. A plurality of parallel data busses are connected to the AC&S circuit 85A.

The output of the DC&T circuit 89A switches the I precision gate driver circuits 86A and 86B and the current slot DMOSFETs 87A and 87B to on and off using precise timing synchronized by the Vsync signal and the gray scale clock (GSK) signal. The current sink DMOSFETs 87A and 87B control the current in the two LED strings (not shown) in response to analog signals from the AC&S circuit 85A, which control the precision circuits 86A and 86B and thus the current sink DMOSFET 87A and Gate drive signal for 87B. The drive gate signals are analogous, and one of the feedback amplifiers is used to ensure that the currents in each of the current sink DMOSFETs 87A and 87B are respectively fixed by one of the reference currents Iref _A and Iref _B also supplied by the AC&S circuit 85A. multiple.

Although FIG. 6 depicts only current slot DMOSFETs 87A and 87B, the circuit shown is compatible with the stacked clamp LED driver 50 shown in FIG. 3A or the high voltage LED driver 80 shown in FIG. 3B. To implement the spliced clamp version, two high voltage N-channel DMOSFETs will be connected in series with current sink DMOSFETs 87A and 87B, wherein the source terminals of the high voltage N-channel DMOSFETs are connected to the current sink DMOSFETs 87A and The 汲 terminal of 87B, and the 汲 terminal of the high voltage N-channel DMOSFET are connected to the anode of the respective LED string being driven.

In operation, the data is clocked into the SLI bus shift register 90A through the sequence input pin SI at the rate of the SCK clock signal. This includes 12-bit PWM with respect to time data entered into registers A and 220B for Channel A and Channel B, and 12-bit phase delay into registers 221A and 221B for Channel A and Channel B. Data, 12-bit "pixel" current data in registers 222A and 222B for channel A and channel B, and 12 bit error information (including 8 bits in the fault setting register 224) And enter the 4 bits in the fault state register 225). As new data is clocked in, the data in these registers is clocked out of the SO pin. Suspending the SCK signal statically stores the data in the displacement registers. The terms "channel A" and "channel B" are arbitrary and are only used to identify the output in the SLI data string and its corresponding data.

After receiving a Vsync pulse, the data from the PWM A register 220A is loaded into the D latch 211A, and the data from the phase A register 221A is loaded into the latch & counter A circuit 210A. Φ latch 212A. At the same time, the data from the PWM B register 220B is loaded into the D latch 211B, and the data from the phase B register 221B is loaded into the Φ latch 212B of the latch & counter B circuit 210B. in. After receiving the subsequent clock signals of the GSC gray-scale clock, the latch & counters 210A and 210B calculate the number of pulses in their Φ latches 212A and 212B, and then cause the currents to be in the I-precision circuits 86A and 86B, respectively. Flowing in, illuminating the associated LED string in channel A or B. The channels remain enabled and conduct for the duration of the number of pulses stored in D latches 211A and 211B, respectively. Thereafter, the output is switched off and the next Vsync pulse is awaited to repeat the process. The DC&T circuit 89A thus synthesizes two PWM pulses to the gates of the DMOSFETs 87A and 87B based on the data in the SLI bus shift register 90A.

Also synchronized with the Vsync pulse, the data stored in the image point A register 222A and the image point B register 222B is copied to the D/A converters 213A and 213B to set the DMOSFET. Current in 87A and 87B. The D/A converters 213A and 213B are discrete circuits that provide an accurate portion of Iref to set the current in the associated LED string. Alternatively, in a preferred embodiment, DMOSFETs 87A and 87B have gate widths that are divided into various segments using binary weighting, and charge the appropriate combination of the gate segments to set the portion of the desired maximum current. The reference current Iref indicating the maximum channel current is set to a reference current source 217 by the Rset resistor 204 and the Vref input.

The fault detection circuit includes an LED fault detection circuit 215 that compares the source voltages of the current sink DMOSFETs 87A and 87B with the values stored in the fault latch circuit 214. The data in the fault latch circuit 214 is copied from the fault setting register 224 at each Vsync pulse. Temperature detection circuit 216 monitors the temperature in LED driver IC 81, which includes the circuitry shown in FIG. A fault detection immediately triggers the open drain fault flag MOSFET 219 to turn "on" and pull the FLT line to a low level, generating an interrupt. The data in the fault latch circuit 214 is written to the fault state register 225 on the next Vsync pulse.

Embodiments of the pixel function and the digital to analog conversion are described in further detail in the above-cited application Serial No. 13/346,625. The application also includes an example of a detailed circuit implementation of fault latch circuit 214 and LED fault detection circuit 215, reference current source 217, and current sense feedback (CSFB) circuit 218.

In the manner described, a sequence of data busses is used to control the current, timing, and duration of several LED strings, as well as to detect and report the occurrence of fault conditions in the LED strings. The SLI protocol is flexible, and only the data sent through the SLI bus displacement register 90A is matched to the controlled hardware. Specifically, the number of bits transmitted by each driver IC matches the required position of each driver IC. The number of bits, and the number of bits sent in a Vsync cycle, matches the number of bits sent by each driver IC multiplied by the number of driver ICs.

For example, in the circuit of Figure 6, the agreement including pixel correction, fault setting, and fault reporting includes 88 bits per dual channel driver IC, i.e., 44 bits per channel or LED string. If the eight dual-channel driver ICs that control 16 LED strings are connected to a single In the SLI bus loop, the total number of bits that move out of the interface IC and pass through the SLI bus in each Vsync cycle is 8 times 88 or 704 bits, less than kilobits. If the SLI bus is clocked at 10 MHz, the entire data stream can pass through each driver IC in 70.4 microseconds and reach each channel, or 4.4 microseconds per channel.

Although the sequence data bus communicates at an "electronic" data rate (ie, using a MHz clock for controlling changes and a Mbit data rate per second, Vsync or "frame rate"), the image on the LCD display panel is Slower speed occurs because the human eye cannot quickly perceive the changed image. Although most people are not aware of the 60Hz frame rate (ie, 60 image frames per second), in the comparison of A to B, for many people, 120Hz TV images look more than 60Hz TV images. Clear, but only use direct comparison. At even higher Vsync rates (eg, 240 Hz and above), only "game players" and video display "experts" claim to see any improvement, mainly due to reduced motion blur. The large ratio between the electronic data rate and the relatively slow video frame rate makes it possible to serial bus communication to the backlit LED driver.

For example, at 60 Hz, each Vsync cycle takes 16.7 milliseconds, which is orders of magnitude longer than the time required to send all data to all of the driver ICs. Even in the most advanced TVs operating at an 8X scan rate and in 3D mode, each Vsync cycle takes 1.04 milliseconds at 960 Hz, meaning up to 236 channels can be controlled in real time. This number of channels greatly exceeds the drive requirements for even the largest HDTV.

Each dual-channel 88-bit complex "contract" used in the SLI bus shift register 90A of Figure 6 enables the interface IC to write or read each register of each channel during each Vsync cycle. All the information inside. The term "complex" refers to the content used to control the digits of each channel. Even if no changes have been made to the previous data packet, the complex protocol requires that each variable and register be specified in each data packet transmitted by the self-interface IC 101 to one of the driver ICs 81A through 81H.

If a reduced data agreement is used (ie, each channel requires less than one of the bits), Sending data to each channel takes even less time. Because this complex protocol does not have timing constraints due to the relatively slow Vsync refresh rate, there is no data rate benefit. However, the use of fewer bits in a serial communication protocol does reduce the size of the bit shift registers and data latches in the driver IC, thereby reducing die area and overall system cost.

For example, one of the SLI busbars using 64 bits instead of 88 bits is shown in the LED driver system 250 of FIG. 7, which includes LED driver ICs 251A through 251H and an interface IC 252. . As shown by data sequence 253, the protocol still uses a 12-bit PWM luminance action time factor, a 12-bit phase delay, an 8-bit fault setting, and a 4-bit fault state, but omits the 12-bit pixel correction data. . Therefore, individual channel current settings and brightness calibration for each LED string are not available in this embodiment.

In the manufacture of LCD panels, many manufacturers believe that the uniform brightness of an electronically calibrated display is too expensive and therefore not commercially viable. The global display brightness can still be calibrated by adjusting the value of a panel current setting resistor (such as the set resistor 204 shown in Figure 6), but the uniformity of the backlight brightness cannot be controlled by the microcontroller or interface IC. Alternatively, panel manufacturers manually "classify" their LED supplies into bins of LEDs with similar brightness and color temperatures.

It should be noted that removing pixel data from the SLI busbar protocol does not prevent overall display brightness control or calibration. Adjusting the system's global reference voltage, Vref, can still perform global dimming and global current control. For example, in the system shown in FIG. 6, the value of the adjusted Vref affects the value of the reference current Iref generated by the reference current source 217. If the reference voltage Vref is common to all driver ICs, then adjusting Vref will be independent of the PWM dimming control, affecting each driver IC evenly and thus affecting the overall brightness of the panel.

Returning to Figure 7, system 250 depicts SLI bus data communication from a common system interface IC 252 to one of the eight driver ICs 251A through 251H. As shown, the SLI bus sequence output SO of the interface IC 252 generates a sequence of pulses and is synchronized to the sequence clock pin. The clock pulses on the SC feed the pulses to the input pins of the driver IC 251A. The SLI bus sequence output of the driver IC 251A then sends its internal shift register data out of the SO pin of the driver IC 251A and to the SI input pin of the driver IC 251B. Similarly, the SO output of driver IC 251B is coupled to the input pins of driver IC 251C, and so on, to form a "digital" daisy chain. The last driver IC 251H in the daisy chain sends its SLI bus data from its SO pin back to the SI pin of the interface IC 252 to complete the loop.

In operation of system 250, interface IC 252 sends data from the interface of IC 252 to the scalar or video IC of the system in response to instructions received on the SPI bus interface of interface IC 252. The SO output for each driver IC and LED string is sequentially clocked to each of the driver ICs 251A through 251H. All data must be sent to all drive ICs in a single Vsync cycle. Since the SLI bus is a sequence agreement, the first data sent from the interface IC 252 represents the bit used to control the driver IC 251H. After 64 clock pulses, the data designated for the driver IC 251H appears in the SLI bus shift register of the driver IC 251A. The interface IC 252 then outputs the data for the driver IC 251G synchronized to the other 64 pulses on the SC clock pin on its SO pin. During these 64 clock pulses, the data for the driver IC 251H is moved from the SLI busbar shift register in the driver IC 251A and temporarily moved into the SLI busbar shift register in the driver IC 251B. This procedure is repeated until finally, and the data for the driver IC 251A synchronized to the last 64 pulses on the SC clock is output on the SO pin of the interface IC 252.

In the last 64-bit "write cycle" of a given Vsync cycle, the data for the driver IC 251A is output from the SO pin and loaded into the SLI bus shift register in the driver IC 251A. The data in the driver IC 251B is moved from the SLI busbar shift register in the driver IC 251A and moved to the SLI busbar shift register in the driver IC 251B, and so on. Similarly, in the last 64 bit periods of the write cycle The data for the driver IC 251H is moved from the SLI busbar shift register in the driver IC 251G to the SLI busbar shift register in the driver IC 251H. Therefore, after 8 x 64 clock pulses or 512 pulses on the SC pin, all data has been loaded into the SLI bus shift register of the corresponding driver IC. However, this information has not yet controlled the operation of the LED string.

Only after the next Vsync pulse is supplied to the driver IC, this newly loaded data is copied from the SLI bus shift register and copied to the active latch of its corresponding driver IC for controlling LED brightness and timing. And fault management. Specifically, the data in the SLI bus register in the driver IC 251A is copied to the active latch that affects the operation of the LED strings controlled by channels A and B, and the SLI busbar displacement in the driver IC 251B The data in the scratchpad is copied to the active latch that affects the operation of the LED string controlled by channels C and D, and so on. Thereafter, the SLI bus displacement registers are ready to be rewritten for new data for the next Vsync cycle. For the remainder of the current Vsync cycle, the LED string will be controlled based on the data received prior to the last Vsync pulse.

In this way, the SLI bus data communication timing and timing are not synchronized with the Vsync period of the system and the Vsync pulse that starts each Vsync period. That is, the data from the interface IC 252 can be sent to the driver ICs 251A through 251H faster or slower through the SLI bus, allowing the viewer of the display to not perceive the ongoing multi-chip interaction or change until the next Vsync occurs. LED settings. The only timing requirement is that the interface IC 252 can receive its instructions from the video controller or the scalar IC via its SPI bus input, interpret the instructions, and on the SO pins of its SLI bus in a single Vsync cycle. Output channel specific information for each driver IC. As previously described, since the time required to receive such instructions is much shorter than the Vsync period, this timing requirement does not impose any restrictions on the operation of the display.

FIG. 7 also illustrates that the fault set data register may include various types of data including a voltage for adjusting a short-circuit LED (SLED code set), and is set to ignore one. One time period of the short-circuit LED detection output fault (short-circuit LED fault blanking), one time period for ignoring the fault of the self-breaking LED detection output (breaking LED fault blanking) and clearing the previously reported disconnection and Short-circuit LED fault register (open circuit CLR and short circuit CLR). The SLI bus bar protocol is not limited to implementing a particular fault related function or feature.

System 250 also illustrates the implementation of the SLI bus as a loop fault readback capability by connecting the SO output of the last driver IC (driver IC 251H) in the daisy chain to the SI input of interface IC 252. When data from the interface IC 252 is written to the driver ICs 251A through 251H, the data resident in the SLI bus displacement register advances through the daisy chain with each SC clock pulse. If the data in the SLI bus displacement register contains fault detection data written by one of the driver ICs 251A to 251H, the data is clocked through the loop and the return interface IC 252 facilitates the driver ICs 251A to 251H. One of the specific fault states is used to report back to the interface IC 252 and route through the SPI to other components of the system. What the interface IC 252 does for fault information depends on its design and is not limited by the SLI bus protocol or hardware.

Multi-channel driver capabilities and limitations

Although the example shown describes a dual channel driver IC, the disclosed driver concept and architecture can be extended to a larger number of integrated channels without limitation, except for power consumption and temperature constraints of driver IC, package and printed circuit board design. .

One example of a multi-channel LED driver consistent with the disclosed architecture is illustrated in FIG. Similar to the dual channel driver of FIG. 3B, the quaternary LED driver IC 301 integrates the four channels of the high voltage current sink DMOSFETs 307A through 307D with the high voltage diodes 308A through 308D, respectively. The current sink DMOSFETs 307A through 307D are controlled by I precision gate driver circuits 306A through 306D to control the currents in LED strings 303A through 303D that are calibrated to a current setting resistor 302. Driver IC 301 (such as other driver ICs in the system) includes a bias supply 304, an analog control and sense (AC&S) circuit 310, and a digital control in time Order (DC&T) circuit 309.

In addition to doubling the number of I-precision gate driver circuits and current-slot DMOSFETs in the dual-channel version, the quaternary LED driver 301 also requires additional latches and circuitry in the AC&S circuit 310 and DC&T circuit 309 to support additional channels. When a temperature protection circuit is sufficient for each driver IC, the temperature protection circuit does not need to be doubled. A significant area is also dedicated to the SLI bus register 311, which must be doubled in size to support four channels instead of two.

One embodiment of a four-channel SLI bus displacement register 311 is shown in FIG. The four-channel SLI bus displacement register 311 contains 176 bits, which is twice the data storage capacity of the SLI bus displacement register 90A of the dual channel system of FIG. Therefore, the entire data stream containing PWM data, phase data bits, and image data and fault data is twice as long, but there is no need to change the SLI bus protocol. Copying some of the fault data (such as temperature fault data stored in the four-bit fault state registers 354 and 355), but the area of the die saved by eliminating redundant bits is generally not worthy of the change agreement. Complexity.

Therefore, by using the "complex" SLI bus protocol for transmitting all the data for each register in the daisy chain, each time data is written from the interface IC 101 to the LED driver ICs 81A to 81H, and only The number of channels integrated into an LED driver IC is expanded by expanding the SLI busbar shift registers 90A through 90H in a ratio to accommodate an appropriate number of integrated channels.

However, this complex SLI busbar protocol has several drawbacks. In particular, even when some of the material has not changed, the interface IC 101 remains cumbersome to repeatedly remove the data onto all of the driver ICs 81A to 81H on the SLI bus 113. Further, the displacement registers 90A to 90H of the multi-channel LED driver ICs 81A to 81H are relatively large, and they occupy a significant grain area.

One of the disadvantages of reducing the size of the data being sent is that the SLI bus protocol overcomes these shortcomings, so that only the latch data that is changed between the video frames needs to be rewritten.

For example, in the LED driver IC 81 shown in FIG. 6, the data loaded into the shift register 90A is written to the latch and counters 210A and 210B, respectively, every Vsync cycle, even if no changes have occurred. The latches 211A, 212A, 211B, and 212B, the D/A converters 213A and 213B, and the fault latch circuit 214 are read from or read at least once. Repeated transmission and retransmission of unaltered data is inefficient, cumbersome and potentially expensive, wastes busbar bandwidth, occupies the system with trivial work, and consumes an area with excessive displacement registers.

Improved sequence illumination interface bus

Preventing the transmission of longer digits on a sequence of busses by adding a "latch address" or "first code" to the sequence illumination interface bus protocol and embedding it in each SLI bus communication Limitations and shortcomings of the instructions. When combined with circuitry to decode and multiplex SLI bus data, the embedded first code information causes the data to be routed only to specific target latches.

By sending the data only to the latches that need to be updated, the "first code multiplex" or "thin" SLI bus architecture avoids the need to repeat and unnecessarily resend digital data, especially if the resend remains constant or Extra information that is rarely changed. In operation, after an initial setting, only the latches that need to be changed are rewritten.

The latch containing the fixed data is written only once when the system is first initialized, and then does not need to communicate with the system IC via the SLI bus. Since only the changed latches are updated, the amount of data sent across the SLI bus is greatly reduced. This approach offers several advantages over the "complex" SLI busbar approach, namely:

● Especially in small (for example, two-channel) LED driver ICs, the number of bits required to integrate an SLI busbar shift register is greatly reduced, saving die area and reducing cost.

● Increase the effective bandwidth of the SLI bus at any given timing rate, because the redundant data is not sent repeatedly.

●SLI bus bar protocol can be standardized with fixed block length and function without losing function Sex

An example of a first code multiplexed SLI bus is shown in the embodiment of LED driver IC 81 shown in the schematic circuit diagram of FIG. In addition to the alternative LED driver IC 81, FIG. 10 also shows an SLI bus 410 including a 16-bit first code register 312 and a 16-bit data register 313, and a first code decoder and multiplexing. (mux) circuit 419. The data in data buffer 313 is routed to latches and counters A 410A and D latches 411A and 411B and Φ latches 412A and 412B in latch and counter B 410B, respectively, to digital control and timing. One of the D/A converters 413A and 413B in the (DC&T) circuit 402, or one of the analog latching and sensing (AC&S) circuits 403. The first code decoder and multiplexer circuit 419 performs such data transfer in accordance with the routing direction included in the first code register 312. Therefore, the first code decoder and multiplexer circuit 419 decodes the 16-bit block stored in the first code register 312 and multiplexes the data stored in the data register 313 to the DC&T circuit 402 and the AC&S circuit 403. In the appropriate D, Φ or pixel latches.

In the case of the fault latch circuit 414, the multiplexer 419 operates bi-directionally, allowing the data stored in the data register 313 to be written into the fault latch circuit 414 or, conversely, to be stored in the fault latch circuit. The data in 414 is written to data register 313.

In the embodiment illustrated in FIG. 10, the first code multiplexed SLI bus protocol uses a 32-bit block, that is, the block stored in the first code register 312 has a length of 16 bits. The length of the block stored in data register 313 is also 16 bits, facilitating the reading of one of up to 65,536 different latches with one of up to 65,536 combinations being uniquely written to or read from. This provides a well-balanced compromise between addressing a large number of latches and maintaining the flexibility of a short block length and the size of a small SLI bus register and providing both flexibility and scalability.

Although a large number of combinations are promoted, it is not necessary to use all of the data in the SLI bus. If LED driver IC 81 contains fewer function latches and channels, then The first codeword group of less than 16 bits is decoded. Similarly, if lower precision is required, a data block of less than 16 bits needs to be transferred to the target latch. For example, if the data contained in the data register 313 is a PWM brightness action time factor, then 12 bit data can be multiplexed and loaded into the D latch 411A, and if the register 313 is present. The data is set for the LED current "image point", and the pixel register associated with the D/A converter 413A requires only 8 bits.

Therefore, in the first code multiplexed SLI bus, the data is repeatedly written into the data register 313 one by one by the interface IC 101, and then the data is multiplexed to the DC&T circuit 402 and the AC&S circuit. One of several function latches in 403. In the embodiment of FIG. 10, the data in data register 313 is spread among seven different functional latches having different functional roles.

The "simplified" first code multiplexed SLI bus bar 410 shown in FIG. 10 is in sharp contrast to the "complex" SLI bus bar 90A shown in FIG. 6, wherein each of the SLI bus bar shift registers 90A is temporarily placed. The memory has a one-to-one correspondence with one of the function latches of the LED driver IC 81. For example, the PWM A register 220A transfers the data to the D latch 211A, and the phase A register 221A transfers the data to the Φ latch. In the device 212A, and so on. This one-to-one correspondence makes scaling the complex SLI busbar architecture to a larger channel number driver IC both problematic and expensive.

The ability to spread the first-code multiplexed SLI busbar thus provides a more functional, lower-cost way to implement a multi-channel LED driver IC than the complex SLI busbar protocol. For the reasons considered below and for other reasons, the first code multiplexed SLI bus represents an improved sequence illumination interface bus protocol, architecture and physical interface.

A further improvement of one of the first code multiplexed SLI busbar methods is illustrated in FIG. In this example, the 16-bit first code register in the SLI bus 311 is further divided into two 8-bit first code registers 312C and 312F, which respectively store channel and function first code information. The data register 313 remains unchanged. As shown, a first code decoder 451 has two outputs, which one to control One of the LED channels selects output 453 and selects one of the function latches (i.e., which function latch is written to or read from) the function select output 452.

The first code decoder 451 selects one of the plurality of channels 457 with one of the channel select signals in the output 453; the first code decoder 451 then selects a function (e.g., PWM or phase) to be controlled with one of the function selection signals in the output 452. A multiplexer circuit 454 then writes the data from the data register 313 into a latch 455 that controls one of the analog or digital functions 456 in the particular channel 457 selected.

In this way, any number of channels (ie, any number of LED strings) within an LED driver IC can be independently controlled in real time, and a common SLI bus bar 311 facilitates precise adjustment of each control function without requiring a large displacement. A scratchpad or a longer digit block.

In a preferred embodiment of the present invention, the first code (ch) register, the first code (fcn) register, and the data register in the SLI bus 311 store 32 bits of one of 16 bit data. The block (ie, 16 bits are unused). The block can therefore address one of the 256 different functions of any of the 256 channels. Since the number of possible combinations greatly exceeds the number of channels and functions required in a single LED driver IC, the improved SLI bus protocol is not limited to the LED driver examples described herein. However, in a single LED driver IC, the number of combinations can be limited by decoding only a subset of the possible digital latch addresses, reducing the size of the associated circuitry to a minimum. Since each LED driver IC requires only one 32-bit displacement register, the additional unused bits in the preferred 32-bit SLI busbar protocol do not waste significant grain area.

As an example of reducing the number of decoded bits, the two least significant bits (LSBs) of the decoding channel first code register 312C and the two LSBs of the function first code register 312F are easily accommodated in FIG. The quaternary LED driver 301 of a 32-bit displacement register is much smaller than the 176-bit displacement register 311 required for the complex SLI busbar protocol, as shown in FIG. The 4-channel LED driver decoding is described in the following list as a possible implementation.

12A illustrates a variation of the embodiment of the LED driver IC 81 shown in FIG. 10. In the embodiment of FIG. 12A, the first code decoder and multiplexer 419 have been divided into a decoder 491 and a multiplexer. 492.

The LED driver IC 81 shown in Figure 12A provides full control of two channels, 12-bit PWM brightness control, and 12-bit phase with 250V LED drive with 150V circuit capability and ±2% absolute current accuracy. Control, 8 bit current control, LED open and LED short circuit fault detection, and over temperature detection, all controlled by high speed SLI bus 410 and with a common Vsync and grayscale clock (GSC) ) The signal is synchronized with other drives. Although the current sink DMOSFETs 87A and 87B shown in Figure 12A have a nominal capability of 150V, such devices can be sized as needed to operate from 100V to 300V. The 250 mA rated current of the DMOSFETs 87A and 87B is set by the power consumption of the driver IC 81 and the mismatch of the forward voltages in the LED strings 83A and 83B. Above 100V rated, it is advantageous to integrate the high voltage cascode clamped DMOSFETs in series with current sink DMOSFETs 87A and 87B, whereby current sink DMOSFETs 87A and 87B do not operate above the clamp voltage provided by the stacked clamp DMOSFETs ( also That is, higher than 12V as described above in connection with FIG. 3A).

In operation, the LED driver IC 81 shown in FIG. 12A receives a data string fed to the SLI bus shift register 410 on its serial input (SI) header. The data is clocked at a rate set by a sequence clock (SCK) signal supplied by interface IC 101 (not shown). The maximum timing rate for this data depends on the CMOS technology used to implement the SLI bus shift register 410, but even with a 0.5 μm line width program and fab, a 10 MHz operation can be achieved. As long as the SCK signal continues to run, the data will move into the SLI bus shift register 410 and eventually exit the sequence output (SO) pin on its path to the next LED driver IC in the sequence daisy chain.

After the data corresponding to the particular LED driver IC reaches the SLI bus shift register 410, the interface IC 101 immediately stops the SCK signal. From the data in the SLI bus displacement register 410, the decoder 491 determines the channel and latch in the DC&T circuit 402 or AC&S circuit 403 to be controlled, and instructs the multiplexer 492 to temporarily store the SLI bus displacement. A data register in device 410 is coupled to the latch. The transfer of data from the data register in the SLI bus shift register 410 to the target latch in the DC&T circuit 402 or the AC&S circuit 403 occurs at the next Vsync pulse. The data latches in the DC&T circuit 402 or AC&S circuit 403 may include flip-flops or static RAM. If the decoder 491 indicates that the SLI bus is interrogating the fault latch in the AC&S circuit 403, then any data previously written to the fault latch in the AC&S circuit 403 is copied to the SLI at the Vsync pulse. The bus shift register 410 is in the appropriate bit.

The recovery of the SCK signal moves the read and write bits in the SLI bus shift register 410 to the lower LED driver IC in the daisy chain. In a preferred embodiment, the daisy chain forms a connection back to one of the loops of the interface IC. Sending new data to the daisy chain ultimately pushes existing data residing in the SLI busbar shift register through the loop and ultimately back to the interface IC 101. In this manner, the interface IC 101 can communicate with individual LED driver ICs, set LED string brightness and timing, and the individual LED driver ICs can communicate individual fault conditions. Return to the interface IC.

The SLI bus data advances by one bit per SCK pulse through the displacement of the displacement register connected to the daisy chain. After 32 SCK pulses, the 32-bit data or "word" used for the last LED driver IC has been removed from the interface IC and moved to the first LED driver IC in the daisy chain, but has not yet resided in the predetermined LED driver IC. After 64 SCK pulses, the first 32-bit block moves from the first LED driver IC to the second LED driver IC, and the next 32-bit block is moved from the interface IC to the daisy chain. The first LED driver IC. At this step, the SLI bus blocks are still not resident in their appropriate driver ICs. In the daisy chain containing "n" SLI bus registers in a daisy chain, the data is finally moved to the appropriate LED driver IC only after "n" is multiplied by 32 sequence clock pulses SCK. Interrupting the SCK pulses copies the data from the SLI bus shift register to the preload latch, as described below in connection with FIG. At the next Vsync pulse, data is copied from the preload latches to the active latch and the LED driver changes take effect. Prior to this, the operation of the LED driver IC remained unaffected.

Due to the two-stage latch architecture, that is, a combination of a pre-loaded latch and a second-stage active latch (described below in connection with Figure 14), the first-code multiplexed SLI bus protocol and interface are relatively robust. It is not affected by the error indicating the LED driver IC. For example, if the SCK pulse stream is stopped immediately before the displaced data resides in its target SLI busbar displacement register and the corresponding LED driver IC, the data will be copied from the SLI busbar shift register to In the preload latch, the active latch data will not be changed until the Vsync pulse occurs. As long as the SCK pulse resumes operation and the shift procedure is completed before the Vsync pulse occurs, no errors will occur due to the sporadic SCK pulse.

In the case where an LED driver IC includes two or more LED channels, the shift procedure must occur multiple times before the Vsync pulse makes the change active. For example, you can load the preload latches of all odd-numbered channels first, followed by the even-numbered All information on the channel. Repeat this procedure for each function until all preload latches have been loaded at least once. After all of the preload latches are loaded, the Vsync pulse initiates a change in the operation of the LED driver IC by copying the preload latch data into the active latch, thereby altering the operation of the LED driver IC. The loading of data into the multi-channel LED driver IC using the first code multiplexed SLI bus protocol is described in further detail later in this application.

Using this timing scheme, data can be shifted through a large number of driver ICs at high speed without affecting LED current or causing flicker because the current and timing of the control current tank DMOSFETs 87A and 87B are only changed after each new Vsync pulse. The frequency of the Vsync pulse can vary from 60 Hz to 960 Hz, with the frequency of the gray scale clock (GSC) signal being scaled (typically 4096 times the frequency of the Vsync signal). Since Vsync is slower (less than 1 kHz) when compared to the SLI bus time SCK frequency, the controller has the flexibility to modify and resend the data, or to query for a fault lock for the duration of a given vertical sync pulse. Save the device multiple times.

Since in the reduced SLI bus protocol, the data registers in the SLI bus 410 are not large enough to be written to all of the functional latches in the DC&T circuit 402 and the AC&S circuit 403 from a single SLI bus block or data packet. Therefore, the interface IC 101 must send multiple SLI bus packets to the driver ICs to load all of the functional latches. This condition occurs at startup, when all latches need to be filled, or when data in more than one latch must be changed at the same time. If it is allowed to gradually change the data of the control I precision gate driver circuits 86A and 86B in a plurality of steps in a plurality of Vsync cycles (for example, first changing the Φ latch, then changing the D latch, and then changing the pixel latch, etc.) ), then a viewer can see the step change as the blinking or noise in the video image. Several solutions to this possible problem are disclosed below under the heading "Loading Multiple Function Latches Simultaneously".

After loading the scratchpad data, starting with the next Vsync pulse, DC&T circuit 402 generates two PWM pulses after the appropriate phase delay and the appropriate pulse width duration. The output of the I-precision gate driver circuits 86A and 86B is switched on and off (or during the time factor D). I precision gate driver circuits 86A and 86B sense currents in current sink DMOSFETs 87A and 87B, respectively, and provide appropriate gate drive voltages during the time when I precision gate driver circuits 86A and 86B are enabled by the PWM pulses of DC&T circuit 402. Maintain a target current. The I precision gate driver circuit thus operates in a manner similar to a "strobe" amplifier that performs digital pulse on and off but controls the current in the LED as an analog parameter.

The peak currents in all LED driver ICs are globally set by the Vref signal and by the value of Iset resistor 82. In a preferred embodiment, the Vref signal is generated by interface IC 101, or it can be supplied as an auxiliary output from an AC/DC converter module. In an alternate embodiment, channel-specific pixel correction can be eliminated, and Vref can be modulated to facilitate global current control of the LED current.

In a driver IC capable of channel-specific pixel correction, the current in any of the LED strings can be controlled by an SLI bus through an image dot latch (preferably including an 8-bit to 12-bit block). The pixel latch adjusts the current of the current sink DMOSFET to one of 0% to 100% of the peak current in 256 or 4096 different steps, respectively. In this way, the newly revealed architecture enables precise digital control of the LED current (a function of a current mode digital to analog converter or "current DAC"). In LCD backlight applications, this feature can be used to calibrate backlight brightness, to improve backlight uniformity, or for operation in 3D mode.

The structure and operation of the I-precision gate driver circuits 86A and 86B and the AC&S circuit 403 are described in application Serial No. 13/346,625.

As shown, the current flowing through LED string 83A is controlled by current sink DMOSFET 87A and corresponding I precision gate drive circuit 86A. Similarly, the current flowing through LED string 83B is controlled by current sink DMOSFET 87B and corresponding I precision gate drive circuit 86B. Maximum power applied to current sink DMOSFETs 87A and 87B without splicing the MOSFET The voltage is limited to operations below the breakdown voltage of the high voltage diodes 88A and 88B. Bias circuit 84 produces an internal wafer bias voltage from a 5V Vcc input.

The drain voltages of current sink DMOSFETs 87A and 87B are also monitored by AC&S circuit 403 and compared to an overvoltage value stored in the latch of SLI bus 410. If the drain voltage is below a stylized value, the LED strings 83A and 83B operate normally. However, if the drain voltages of current sink DMOSFETs 87A and 87B rise to about a programmed value, one or more of LED strings 83A and 83B are shorted, and one of the particular channels is detected and recorded as a fault. Similarly, if one or more of the I precision gate driver circuits 86A and 86B are unable to maintain the required current (ie, the LED string is operating in the "under current" condition), this means that an LED is not turned on and loses the circuit. Continuity. The channel is then closed, the CSFB signal for that channel is ignored, and the fault is reported. The "current" can be sensed by monitoring the output saturation of the I-precision gate driver circuits 86A and 86B (meaning that the gate driver circuit drives the gate of the current-slot DMOSFET as "fully-on" as possible). Insufficient, or alternatively, this "out of current" can be sensed by monitoring the voltage drop across the input terminals of the I precision gate driver circuit. When the voltage to the input voltage to the I-precision gate driver circuit drops too low, an under-current condition indicating a broken-circuit LED fault has occurred.

If an over-temperature condition is detected, a fault is reported and the channel remains on and conducted unless the interface IC 101 sends a command to close the channel. However, if the temperature continues to rise to a dangerous level, the AC&S circuit 403 will independently deactivate the channel and report the fault. Regardless of the nature of the fault (a shorted LED, a broken LED, or an overtemperature condition), as soon as a fault occurs, one of the open MOSFETs in the AC&S circuit 403 will activate the FLT pin and pull the FLT pin to a low level. A situation in which a fault condition has occurred is signaled to the host μC 152.

The AC&S circuit 403 also includes an analog current sense feedback (CSFB) signal that monitors the drain voltage of the current sink DMOSFETs 87A and 87B and the voltage at the CSFBI input pin of the LED driver IC 81, with a minimum of the three voltages. The voltage is passed to the CSFBO output pin of the LED driver IC 81. In this manner, the lowest drain voltage of any of the current sink DMOSFETs, and thus the LED string with the highest forward voltage drop, is passed to the input of the next LED driver IC and ultimately returned to the SMPS 108 of the system for The V _LED supply rail 110 is powered.

In the manner described, a two-channel LED driver IC 81 with integrated dimming and fault detection capabilities can be implemented without the need for an interfacing IC.

FIG. 12B illustrates extending the disclosed first code multiplex SLI bus control method to a four-channel LED driver IC 501. As shown, LED driver IC 501 includes four current sink DMOSFETs 507A through 507D having corresponding I precision gate driver circuits 506A through 506D for independently driving four LED strings 503A through 503D. In the four-channel LED driver IC 501, the DC&T circuit 509 and the AC&S circuit 510 control the four I-precision circuits 506A-506D to double the number of function latches of the two-channel driver.

The 32-bit long SLI bus shift register 512 is loaded multiple times in this example to transfer the necessary data to the various latches in the DC&T circuit 509 and AC&S circuit 510. For example, if each channel includes four latches (ie, D latch, Φ latch, pixel latch, and fault latch), and the driver IC includes four channels, the SLI bus 512 must It is loaded 16 times to set all function latches. Each time data is moved to the SLI bus shift register 512, and the decoder 513 interprets the first code to select the target channel and function, thereby routing the data through the multiplexer 511 to the DC&T circuit 509 and the AC&S circuit 510. Appropriate latch.

Since in the reduced SLI bus protocol, the data register in the SLI bus interface 512 is not large enough to write all function latches from the DC&T circuit 509 and the AC&S circuit 510 from a single SLI bus block or data packet. Therefore, the interface IC must send multiple SLI bus packets to the driver ICs to load all of these latches. This condition occurs at startup, when all function latches are initialized first, or when data in more than one function latch must be changed at the same time. If allowed in multiple steps within a few Vsync cycles Gradually changing the data of the control I precision gate driver circuits 506A to 506D (for example, first changing the Φ latch, then changing the D latch, and then changing the pixel latch, etc.), then a viewer can follow the video image The flashing or noise in the middle sees the step change. Several inventive solutions to prevent this possible problem are disclosed below.

After loading the latch data, starting with the next Vsync pulse, the DC&T circuit 509 generates four independent PWM pulses to switch the I precision gate after the appropriate phase delay and the appropriate pulse width duration (or duration of action factor D). The outputs of driver circuits 506A through 506D are on and off. The I precision gate driver circuits 506A through 506D sense the currents in the current sink DMOSFETs 507A through 507D, respectively, and provide the appropriate gate drive voltage to maintain a target current during the time that the I precision gate driver circuit is enabled by the PWM pulse. The operation of the I precision gate driver circuit is therefore similar to the operation of a "strobe" amplifier that performs digital pulse on and off but controls the current in the LED as an analog parameter. The LED current can be controlled through the SLI bus through the image dot latch, globally through the Vref voltage input, or through a combination of the two.

Figure 12C shows an alternate embodiment of a four channel LED driver. LED driver IC 531 incorporates two 32-bit SLI bus shift registers 542A and 542B to facilitate parallel (i.e., simultaneous) loading of two functional latches. Each of the SLI bus displacement registers 542A and 542B has its own first code and its own associated decoders 543A and 543B. The data is routed through a dual channel multiplexer 541 to appropriate function latches in DC&T circuit 539 and AC&S circuit 540. Otherwise, the operation of the driver IC 531 is similar to the operation of the driver IC 501 in FIG. 12B. The advantage of using a dual SLI bus interface is that the interface IC can be loaded into all of the function latches in the LED driver IC in half of the SLI bus write cycles. Since the same number of bits (i.e., a fixed number of one-half of a 32-bit block or a 64-bit block) is conveyed on the SLI bus, the actual system speed in either method is similar. The main advantage of this method is that the interface IC does not have to manage many small SLI bus communication.

Decoder and multiplexer implementation

As shown in the circuit diagram of FIG. 11, the requirements of the first code multiplexed SLI bus protocol and the interface are decoder and multiplexer functions. Responsible for distributing the data from the SLI bus shift register 311 to the appropriate function latches (ie, a latch 455), the first code decoder 451 interpreting the first code on each new digit block and The multiplexer 454 is instructed to copy the data from the SLI bus data register 313 into the corresponding function latch 455.

One embodiment of this decoder and multiplexer function is shown in FIG. 13A, wherein a first code multiplexed SLI bus 311 is controlled by a decoder 601 and a digital multiplexer 604 of decoding keys 605C and 605F. The data is sequentially distributed to a plurality of libraries 607 of function latches. The functional latches of the banks and their associated sets of latches 606 independently control separate I precision gate driver circuits (not shown) that drive different LED strings. Specifically, the function latch 606 includes channel A latches A1 to A8, channel B latches B1 to B8, channel C latches C1 to C8, and channel D latches D1 to D8, which are formed together. 8 latches of 4 channels for a total of 32 function parameters. For the sake of brevity, only the latch A1 is shown.

A multiplexer 604 for routing digital data between the SLI bus and the channel and function operates in a manner similar to one of a multi-throw switch to facilitate multiple self-SLI bus data registers. An optional data path from 313 to function latch 606. In this example, multiplexer 604 includes four 12-pole, 8-throw or 12P8T switches that are commonly controlled by decoder 601. As shown, in this embodiment, only a portion of the possible combinations of blocks stored in the SLI bus displacement register 311 can be selected.

In particular, since the multiplexer 604 has only 12 "poles" or parallel circuits, the multiplexer 604 passes only 12 facts despite the fact that the data shift register 313 contains a higher resolution 16-bit block. The bit data is to latch 606. Using only 12 bits from a 16-bit block, only 4 of the 65,536 combinations are decoded, or only 6% of the possible combinations. However, in most lighting applications, eight to twelve bits are sufficient to perform the function with the desired accuracy. In general, PWM brightness "D" and phase delay "Φ" require 12-bit precision. Degree, while pixel correction requires only 8-bit precision.

Since multiplexer 604 addresses 4 channels with 8 locations, only 32 latches can be accessed, although first code registers 312C and 312F can address 65,536 different channels and parameters. Thus, a four-element channel eight-position switch accesses 32 combinations, or five bits can be selected from a 16-bit first-order code. This embodiment uses a combination of less than 0.05% of the first code. Since only a small portion of the data in the shift register 311 is used, the multiplexer circuit 604, which uses a relatively low number of logic gates and transistors, occupies a very small grain area.

The decoder 601 includes 12 magnitude comparators (four for channel selection and eight for function selection), and 32 digital logic gates 603 to decode a portion of the SLI bus header code 312 and thereby control more The device 604 selects the channel.

Specifically, in order to uniquely select four channels, it is necessary to decode a 2-bit first code from the channel first code register 312C. Each of the two least significant bits in the channel first code register 312C is correctly matched to the two least significant bits of the channel select code key 605C each time by outputting a logic high or a binary "1" The magnitude comparator 602C performs channel decoding. The truth table for the two-channel magnitude comparator 602C is shown in Table 1:

Since there are four combinations of channel first codes, there are four different magnitude comparators 602C having the same input but having four different outputs, only one of which can have any given time A logical "1" output. Since the above, only one "00" code starts channel A, only one "01" code starts channel B, a "10" code is needed to select channel C, and an "11" code is needed to select channel D. In this way, there is only one SLI bus header code combination to select a given channel. In the 2-bit decoder shown, only the two least significant bits are decoded, completely ignoring the bits of the higher magnitude.

In a similar manner, to uniquely select one of the eight function latches, a 3-bit first bit code needs to be decoded from the function first code register 312F. Each of the three least significant bits in the function first code register 312F is correctly matched to the three least significant bits of the function selection code key 605F each time by outputting a logic high or a binary "1" The value comparator 602F performs function decoding. The truth table of the three-channel magnitude comparator 602F is shown in Table 2:

Since there are eight combinations of functional first code codes, there are eight different magnitude comparators 602F having the same input but having four different outputs, only one of which can be at any given time. Has a logical "1" output. From the above, only one "000" code starts function #1 (for example, the action time factor D), only one "001" code starts function #2 (for example, phase delay Φ), and so on. In this way, there is only one SLI bus header code combination to select a given function. In the 3-bit decoder shown, only the three least significant bits are decoded, completely ignoring the bits of the higher magnitude.

The implementation of the magnitude comparator can use Boolean logic (where decoder 601 is hardwired with channel and function code keys 605C and 605F), use counters, or can be stored in a program containing SRAM or even E ² PROM. The memory elements are implemented in various ways. In one embodiment of the present invention, the magnitude comparator is implemented using the circuit shown in FIG. 13D, and FIG. 13D illustrates the three-channel magnitude including three dual-input mutually exclusive NOR gates 632 to 634 and three-input AND gates 635. Comparator 631. An embodiment of a mutually exclusive OR and its inverted counterpart (a mutually exclusive NOR or XNOR gate) is known in the art (see, for example, http://en.wikipedia.org/wiki/XOR_gate).

When the two inputs are the same each time (both are "0" inputs or both are "1" inputs), the logical truth table of the two-input XNOR function will produce a "high" or logical "1" output. This is shown in Table 3:

For this reason, the mutually exclusive NOR function is logically used to compare bits in two registers, which is actually a digital version of a comparator. To utilize a logical XNOR gate, a multi-bit block must use multiple XNOR gates for bit-to-bit comparison. For example, to check if two 8-bit digits are identical, eight XNOR gates must be used to individually check the bits. In order for two digit blocks to match, all corresponding bits must match. By performing an eight-input logical AND function on all XNOR outputs, one of the AND gates positive outputs can confirm a match.

This method is shown in decoder 631 in FIG. 13D, where three mutually exclusive NOR gates 632 through 634 are used to compare the bits in the SLI bus header code register with the channel or function selection key code table 636. Corresponding bit. For example, XNOR gate 632 compares the least significant bit in the SLI bus header code with the least significant bit of select code key 636 and matches only them (both have a logical "0" state or both) A logical "1" state outputs a logic "high". The XNOR gate 633 similarly compares one of the least significant bits (i.e., LSB+1) below the first code of the SLI bus with the corresponding bit in the code key 636 and outputs a "high" only when it matches. In a similar manner, comparator 631 compares whether the next least significant bit of the two registers matches. The output of the AND gate 635 will become "high" only if all three bits in the SLI bus header code match, indicating that the two octets are correctly matched. Otherwise, the output of the AND gate 635 and the output of the magnitude comparator 631 will remain "low".

For the sake of brevity, we use a reference number set 637 to represent a multi-channel magnitude comparator (MC) gate, wherein each pair of outputs is compared to each other for matching, and then the results are delivered to a logical AND gate. A table of truth values for a three-input MC gate is described in Table 4, where "1" indicates a match and "0" indicates no match:

The output of the magnitude comparator 637 is "high" only if the magnitudes of the two digits are correctly matched (bitwise confirmation). In the Boolean logic, the magnitude comparator 637 is described as , where SLI _LSB+2 , SLI _LSB+1, and SLI _LSB represent the three least significant bits of the decoded SLI bus first code, and KEY _LSB+2 , KEY _LSB+1, and KEY _LSB indicate channel or function selection code The three least significant bits of the key. In algebra, the plus sign in a circle is a Boolean symbol representing a logical XOR, and. Represents a logical AND, where NOT is a logical inversion, that is, a round plus sign preceded by NOT indicates a logical XNOR.

Returning to Figure 13A, decoder 601 checks one of the four possible channels with MC 602C, and checks one of the eight possible functions with MC 602F, and then performs logic of one of these results using 32 different two-input AND gates 603. AND. At any given time, only one AND gate 603 has a "high" output. This high output turns on a group 12 of transfer MOSFETs in the multiplexer 604 that connects the SLI data register 313 to the corresponding latch 606 in the desired channel. As with multiplexer 604, decoder 601 is simplified in Figure 13A for the sake of brevity.

A more detailed description of one of the decoder 601 and the multiplexer 604 is illustrated in FIG. 13E, wherein the SLI bus channel first code is decoded by the four magnitude comparators 641A through 641D to produce a decoded channel bus 647, and The SLI bus function first code is decoded by the eight magnitude comparators 642A through 642H to produce a decoded function bus 648. These 12 bus bars collectively feed a series of 32 dual input logic AND gates 643A1 through 643A8, 643B1 through 643B8, 643C1 through 643C8, and 643D1-643D8, which in turn drive MOSFETs including multiplexer functions.

Each AND gate 643 combines two inputs, one from one of the four-channel bus bars 647 and the other from one of the eight-function bus bars 648. Since only one channel bus bar 647 is "high" at any time and each of the four channels can have only one of the eight function bus bars 648 as "high", only 32 combinations are decoded. Decoded by the logical AND gate 643A1, this combination combines one of the inputs from the channel A of the bus 647 (ie, the output of the MC 641A) with the second input of the PWM brightness control function "D" from the bus 648 (also That is, the output of MC 642A). Thus, this channel decodes the PWM brightness control for channel A. In a similar manner, the output of channel MC 641B and function MC 642A feeds AND gate 643B1, the output of which is uniquely selected for PWM brightness control of channel B.

As shown, the AND gate 643A2 decodes the phase function Φ for channel A. If the SLI bus header code selects this combination, both outputs of the magnitude comparators 641A and 642B are "high" such that the output of the AND gate 643A2 is also high. The output of inverter 644A then becomes "low" (i.e., near one ground potential), thereby turning on twelve P-channel MOSFETs 645A through 645L. MOSFETs 645A through 645L together act as a multi-channel transfer gate for connecting SLI bus data register 313 to function latch 626A through data bus 649.

A multi-line connection between the SLI data register 313 and the function latch 626A occurs by a one-to-one correspondence between the equally significant bits, where two corresponding LSBs are connected and two LSB+1s are connected And so on. As an example, MOSFET 645A connects b ₁ (the LSB bit on the data bus) to the LSB in latch 626A. Similarly, MOSFET 645L connects b ₁₂ on bus 649 to the most significant bit or MSB in latch 626A. Bus bars b ₂ through b _{11 are} likewise connected in a one-to-one correspondence through ten intermediate MOSFETs (not shown) to their respective bits in latch 626A. Despite the fact that the SLI bus data register 313 includes a 16-bit alphanumeric block, the destination latch 626A is only 12 bits wide. By copying from LSB and up, the twelve least significant bits b ₁ through b ₁₂ are copied from the data register 313 into the latch 626A, ignoring the four most significant of the shift registers 311. Bit. Source register 313 and destination latch 626A need not have the same bit width.

Similarly, AND gate 634D8 decodes the fault data for channel D. If the SLI bus header code selects this combination, the outputs of the magnitude comparators 641D and 642H are both high, so that the output of the AND gate 643D8 is also high. The output of inverter 644B then goes low (i.e., near one ground potential), thereby turning on eight P-channel MOSFETs 646A through 646H. The MOSFETs 646A through 646H together act as a multi-channel transfer gate for the SLI busbar shift register 313 to be coupled to the function latch 626B through the data bus 649. As in the previous example, multiple MOSFETs (eight in this case) interconnect register 313 and data bus 649 to corresponding bits within latch 626B.

In particular, MOSFET 646A connects b ₁ (the LSB bit on the data bus) to the LSB in latch 626B. Similarly, MOSFET 646H so on the bus ₆₄₉₈ b is connected to the latch 626B in the MSB or MSB. Bus bars b ₂ through b _{7 are} likewise connected in a one-to-one correspondence through six intermediate MOSFETs (not shown) to their respective bits in latch 626B. Despite the fact that the SLI bus data register 313 includes a 16-bit alphanumeric block, the destination latch 626B is only 8 bits wide. By copying from LSB and up, the eight least significant bits b ₁ through b ₈ are copied from the data register 313 into the latch 626B, ignoring the eight most significant bits in the shift register 311. Yuan (including MSB). Source register 313 and destination latch 626B do not share the same bit width with each other or with latch 626A.

In this way, even when the function latches do not have the same size as the SLI bus data, the 16-bit SLI bus data can be directed to a specific LED driver through a code multiplex SLI bus. Function latch. In contrast, FIG. 13A depicts the operation of decoder circuit 601 and multiplexer circuit 604 as a high level construction including four magnitude comparators for channel selection and eight magnitudes for function selection. Comparator and 32 The AND gate uniquely drives the transfer gate MOSFET in the quaternary 12P8T multiplexer switch 604. Figure 13E thus depicts one possible embodiment of the system shown in Figure 13A.

It is reiterated that the circuit shown in FIG. 13A and the embodiment of the circuit shown in FIG. 13E illustrate an SLI bus multiplexer LED driver system that independently controls one of the 32 parameters. Since 2 ⁵ = 32, only ⁵ bits of the 16-bit SLI bus header code registers 312C and 312F are needed to provide the data needed to control a 32-parameter LED driver. The remaining I1 bits in the SLI bus first code registers 312C and 312F are ignored. Although the size of the SLI bus displacement register can be reduced, the area saved by the reduced SLI bus displacement register is also smaller than the size of the decoder. An elastic SLI busbar protocol can be implemented in a relatively small amount of area by decoding only the desired combination.

Although this example of a multiplexed SLI bus uses one of the 16-bit first codewords stored in an 8-bit channel first code register 312C and an 8-bit function first code register 312F, It will be apparent to those skilled in the art that a smaller number of bits can be used, and the channel first code register and the function first code register need not be equal in size. For example, an 8-bit meta-address register can utilize a 5-bit channel first-code register to address 32 channels, and utilize only a 3-bit function first-code register to address eight functions. It would be advantageous to prove that, for example, up to 256 separate channels were supported in an LED wall signage application, the channel first code register would require one octet. The use of an additional four bits for function decoding supports 16 functions, which is generally sufficient for most LED lighting and display applications. However, reducing the advantages of the aforementioned 16-bit SLI bus header code to a 12-bit displacement register provides a minimum area of savings. In addition, a 12-bit block is not a power of 2 and is therefore inconsistent with binary and hex data sets and other industry standard communication protocols.

Therefore, while reducing the size of the SLI bus first code register and associated shift register provides minimal savings while sacrificing the flexibility and scalability of the SLI protocol, the number of decoded combinations is minimized and reduced. The size of the multiplexed data bus can really save costs.

For the sake of completeness, other decoding examples are also included. FIG. 13B illustrates driving 16 functional latches by decoding one of the 2-bit channel keys stored in a register 615C and one of the 2-bit function keys stored in a register 615F with the MC 612C and 612F. One of the decoders 616 is a decoder 611 and a multiplexer 614, wherein 16 logical AND gates 613 drive a quad 12T4T multiplexer 614 to facilitate independent routing of 12-bit data to 16 function latches. The data stored in a data buffer 313 is routed to a suitable one of the latches 616 using the first code data stored in a channel first code register 312C and a function first code register 312F.

FIG. 13C illustrates driving eight functional latches by decoding one of the 1-bit channel keys stored in a register 625C and one of the 2-bit function keys stored in a register 625F with the MC 622C and 622F. The decoder 621 is a decoder 621 and a multiplexer 624, wherein the eight logical AND gates 623 drive a dual 12P4T multiplexer 624 to facilitate independent routing of 12 bits of data to the eight function latches. The data stored in a data buffer 313 is routed to the appropriate one of the latches 626 using the first code data stored in the channel first code register 312C and the function first code register 312F.

In the disclosed manner, a multiplexed LED driver can achieve dynamic independent control of multiple LED strings through an elastic sequence communication interface. By using an LED driver IC to multiplex and route data contained in a sequence of communication shift registers to various function latches, flexible control can be achieved without the need for expensive high pin count packages, large area shift registers Or high data rate communication bus or excessively complex control.

Synchronously load multiple function latches

Although the disclosed SLI bus interface and protocol facilitates flexible multi-channel LED driving in low pin count packages, the foregoing implementation is still limited by its inherent two-level register-latch architecture. As shown in Figures 10 through 13, in a two-level register-latch architecture, control data exists only in two latches: one of the SLI bus shift registers and the active function latch . For example, in FIG. 11, the shift register 311 includes SLI bus communication data, and the function latch 455 includes an operation for controlling the operation of the LED driver IC. Functional data.

In the previously described operation, each time a Vsync clock pulse occurs, the data is copied from the shift register 311 to the latch 455. With this simple control method, loading multiple latches can take several Vsync clock cycles. For example, in the first cycle, the SLI bus data is written to the PWM brightness "D" for channel A, and in a second cycle, the data is written to the brightness "D" for channel B, In a third cycle, the SLI bus data is written to the phase delay latch for channel A, and so on. Considering that each channel requires D, Φ, pixel and fault settings, and fault reporting, a dual channel LED driver IC requires at least ten Vsync cycles to load all latches.

In the two-level register-latch architecture, the latch data becomes active immediately after being loaded into the latch at the Vsync pulse. In this context, the term "active" means that the LED drive state is affected by changes in the latch data (ie, the display backlight state has changed), which can cause visible changes in the backlight of the display. Therefore, after loading the channel A luminance data, waiting for the other two Vsync pulses before loading the corresponding channel A phase data means that channel A will drive its LED string with the appropriate brightness but the wrong phase for a period of time.

Writing the change to the function latch in several stages can cause visible aberrations in the backlight, including ghosting, flickering, and the like. Unfortunately, the sequence of non-synchronous loading of function latches in a two-tier register-latch system is inherently problematic. Since there is no temporary storage location to save the data, there is no way to load the data from the interface IC into the driver IC. Therefore, the knock-on effect of sequence changes cannot be avoided. The SLI Bus Displacement Register cannot save data because it must be used to time more data. The function latch cannot be used because it is active and changes the LED drive state when it is loaded.

The solution to this problem is to utilize a three-level scratchpad-latch architecture as shown in FIG. The architecture includes a single SLI bus shift register 311, a plurality of preload latches 655, and a plurality of active function latches 656 coupled to control function 657. Control work Energy 657 can be analogous or digital. In this embodiment, only one SLI bus displacement register 311 is used to sequentially write data to a plurality of preload latches 655. In addition, in the embodiment of FIG. 14, there is a one-to-one correspondence between each preload latch 655 and each active latch 656, although this correspondence may not exist in other embodiments.

The architecture with three levels of registers/latches shown in Figure 14 is not meant to be exhaustive or limiting, but is merely illustrative. For example, an LED driver IC can include more than one SLI bus register, whereby one SLI bus shift register addresses a set of preload latches, and a second SLI bus register addresses a second Group preload latches. However, in general, for economically advantageous multiplexing, the number of active latches 656 should equal or exceed the number of preload latches 655; otherwise, the first code SLI busbar architecture is actually more complex than the complex SLI The row architecture is not cost effective and expensive.

Similarly, although the number of preload latches 655 is equal to the number of active latches 656 in FIG. 14, in other embodiments, the number of preload latches 655 can be less than the number of active latches 656. . Since the primary function of a preload latch is to buffer the data in order to prevent the data from affecting the state of the LED driver, while allowing the data to be written to the associated active latch when needed (not necessarily at the instant of a Vsync pulse) Care must be taken to prevent the aforementioned flicker problem from occurring due to the omission of the preload latch 655 from some channels. Some functions are not sensitive to this flicker problem, for example, the fault set and fault status latches can be written and queried in real time without problems. In fact, the fault latch does not need to be synchronized to the Vsync pulse because the management fault is not related to frame-by-frame image control and backlight status. Similarly, if the image dot latch is only written once during startup, the preload latch for the pixel function can be omitted. In some examples, a preload latch can be shared among several active latches. For example, if the pixel function is only used as a global setting but not for channel-by-channel control, a preload latch for pixel data can be used to write active latches for multiple channels to set the LED current.

In summary, the number of preloaded latches should be equal to or less than the active The number of latches and the number of SLI bus shift registers should be less than the number of preload latches. In a preferred embodiment, at least the channel PWM luminance function or the "D" data, and the phase delay function or "Φ" data should include a three-level register including both the active latch and the pre-load latch - Latch method.

With continued reference to FIG. 14, the basic operation of the three-level register-latch architecture involves moving data into the SLI bus shift register 311 to write data from the SLI bus data register 313 to The data in the corresponding active latch is changed in one of the preloads 655, and the program is repeated for each channel and function until all preload latches are loaded, then at a specified time (For example, at the time of the Vsync pulse), the data from the preload latches 655 is copied into their respective active latches 656. The LED drive status changes only when the active latch data changes. As long as the Vsync pulse does not occur, the preload latch can be written and rewritten multiple times without affecting the LED drive state.

There are various timing options for writing data in the three-level scratchpad-latch architecture: whether data is loaded into the SLI bus shift register 311 and copied to the preload lock within several Vsync cycles All data is loaded in memory 655, or in a single Vsync loop. In any event, it is preferred to copy the data from the preload latch 655 to the active latch 656 at the beginning of a Vsync cycle such that the PWM dimming and phase delay operations remain constant within a video frame and with their predecessors ( The operation of the complex SLI bus version is consistent. In a preferred embodiment, all of the data is written to various preload latches 655 in a single Vsync cycle so that no particular timing issues need to be considered.

One example of an SLI bus communication sequence for loading each preloaded latch of each channel into a display LED backlight system in a single Vsync cycle is illustrated in FIG. The 16-channel display system includes a total of eight LED driver ICs 701A through 701G that drive 16 LED strings, each of which has two channels and individual latches for controlling PWM brightness, phase delay, pixel current setting, and faults. News. For convenience, Sixteen channels are uniquely identified, channels A and B correspond to LED driver IC 701A, channels C and D correspond to LED driver IC 701B, and so on, until driver 701G includes channels P and Q.

Channel O is excluded from the continuous mark to avoid confusion between the letter "O" and the number "0". The total number of latches includes a total of eight driver ICs multiplied by two channels per driver IC multiplied by four latches per channel for a total of 64 latches. Each driver IC includes two channels with four function latches or a total of eight latches, consistent with the dual channel driver and decode architecture shown in Figure 13C. Since each driver IC contains only one SLI bus shift register and eight function latches, it takes at least eight cycles to load data into the entire backlight system, indicated by successive data sequences 702 through 709.

In the example shown, the first data sequence 702 contains data for the fault latches of channels Q, N, L, J, H, F, D, and B in sequence, where the FLT data set is moved to the SLI sink. The row passes through and is then copied into the corresponding fault preload latch. Next, a second data sequence 703 includes data for the fault latches of the channels P, M, K, I, G, E, C, and A, wherein the FLT data set is moved to and passed through the SLI bus. And then copied to the corresponding fault preload latch.

Then, in the data sequence 704, the image data is sequentially loaded for the channels Q, N, L, J, H, F, D, and B, followed by the data sequence 705, in which the image data is sequentially loaded for Channels P, M, K, I, G, E, C, and A. Similarly, in the subsequent data sequence 706, the phase data for channels Q, N, L, J, H, F, D, and B are sequentially loaded, followed by the data sequence 707, which is loaded for channel P, Phase data of M, K, I, G, E, C, and A. Finally, in the data sequence 708, the PWM data for the channels Q, N, L, J, H, F, D, and B are sequentially loaded, followed by the data sequence 709, which is sequentially loaded for the channels P, M, PWM data for K, I, G, E, C, and A. In this manner, each of the driver ICs 701A through 701G is loaded using a single shared SLI bus and multiplexed to its appropriate latch using the appropriate first code, thereby Vsync Load all the data in the ring. Then, at some later time, a Vsync pulse occurs, loading the preload latch data into the active latch, changing the LED drive state and the operation of the display backlight.

It should be noted that although the above sequence is described as writing data from the interface IC to its satellite LED driver IC via the SLI bus, the agreement also supports two-way communication from the LED driver IC back to the interface IC. For example, when data in the data sequence 702 is written to the FLT latch, the fault status information can be copied back from the driver IC to the appropriate bit in the data field of the SLI bus shift register. Then, when the FLT data in the data sequence 703 is removed from the interface IC to the LED driver IC, the fault data residing in the SLI bus displacement register is removed from the SO pin of the last driver IC in the daisy chain and returned to The interface IC is to be interpreted. Therefore, not during the SLI bus broadcast of the data sequence 702, but during the broadcast of the subsequent data sequence 703, the faults for the channels Q, N, L, J, H, F, D, and B are received by the interface IC. Status data. In a similar manner, not during the SLI bus broadcast of the data sequence 703, but during the broadcast of the subsequent data sequence 704, the channel P, M, K, I, G, E, C and A fault status data of A.

In this example, all preload latches in the entire system are written in a single Vsync loop, and when subsequent Vsync pulses occur, the data thus written is transferred from the preload latches to the active Latches. Although this procedure can be repeated for each frame and Vsync pulse of the display operation, resending the excess data after the initial setting of the backlight driver system is neither necessary nor even cumbersome.

One of the calculations and power saving alternatives for overwriting each latch in each Vsync cycle is illustrated in the flow chart and state diagram shown in FIG. 16A. In this flow chart, the backlight control sequence includes two periods: 751A to initialize the backlight LED driver and 751B to refresh the backlight LED driver state. As in the sequence shown in Figure 15, the initialization period 751A involves the use of a sequence clock SCK signal for a given active latch (754). The material (including the first code data and function data) is moved to the (752A) SLI bus and then loaded with the appropriate preload latch (753A). This procedure is repeated with data for each active latch (754) until all preload latches (753A) are loaded. The command to copy data from the SLI bus to a preload latch (753A) can be embedded in the sequence clock SCK waveform and thus does not require a separate hardware solution or wiring. After all of the preload latches (753A) are initialized, the Vsync pulse tells the LED driver IC to copy the data into the active latch (754) and change it, thereby changing the LED drive state and operation of the display backlight.

After initialization, only the function latches that need to be changed are updated and rewritten (ie, rearranged). The update backlight period 751B illustrates that during a data rearrangement, only a particular latch is rewritten by: shifting the data (752B) into the SLI bus under the control of the sequence clock SCK signal, and then Updated channel and function data is only loaded into the specific preload latch (753B). Other preload latches (ie, unupdated latches) remain unchanged. For example, the PWM and phase data for each channel can be updated frequently, but the image data can remain unchanged unless the TV changes from 2D mode to 3D mode or vice versa. In this way, the size of the material that is repeatedly broadcast on the SLI bus is a small portion that is sent during initialization.

In one embodiment of the invention, the instructions for copying data from an SLI bus data register to a preload latch are based entirely on the waveform of the SCK sequence clock signal. In the timing diagram of FIG. 16B, the sequence clock SCK signal 711 operates in a continuous manner while data is loaded into the LED driver ICs 701A through 701H. Since the data is a continuous sequence, the first data moved to the SLI bus bar corresponds to the driver IC farthest from the interface IC (ie, the driver IC 701H), and is moved to the last data in the SLI bus bar. The driver IC closest to the interface IC (ie, driver IC 701A). After the data has been moved to all SLI bus displacement registers in drive ICs 701A through 701H, the SCK signal remains high for a duration t _latch 774 after which all different SLI sinks are coming from. The data of the row shift register is copied in parallel to the preload latch 773. The duration t _latch can be easily implemented with a timer and, for convenience, can be equal to approximately 10 to 20 SCK pulses. For example, if the sequence clock is running at 10 MHz, the duration of each SCK pulse is 0.1 microseconds. If the SCK signal is detected to remain high, the data from the SLI busbar shift register will be latched into the preload latch 773 after the t _latch timer has been clocked for approximately one microsecond.

The timing of the t _latch timer is not critical. In fact, the data accuracy of the SLI bus is not sensitive to the interruption of the SCK signal. For example, if the data is only shifted through one-half of the sequence chain when the SCK signal is temporarily in a "high" state for any reason, the high state will be interpreted as one of the instructions to write data to the preload latch. . Since there is an error data in the SLI bus displacement register at this time, or more accurately, the data is incorrectly located in the SLI bus register, the error data will be latched into the preload latch 773. . Despite this temporary communication error, as long as the Vsync pulse does not occur when the data is in an inappropriate SLI bus shift register, it will not cause system operation problems.

There is no Vsync pulse, ie no preload data is copied into an active latch. Assuming the SCK signal resumes counting, the SLI bus data will continue to be displaced through the sequence bus until it reaches its final destination LED driver IC Displacement Register, after one of the t _latch durations, SLI from the driver ICs 701A through 701H The bus shift register loads the appropriate data into the preload latch 773 to overwrite the incorrect data. Since the entire event occurs within a single Vsync pulse, the fact that the error data is temporarily loaded into the preload latch is completely harmless and unobservable in backlight operation.

To move the SLI bus data to the appropriate IC, one of the key aspects of the SLI bus operation is that the number of bits broadcast on the SLI bus must correspond to the corresponding LED driver IC. For example, in Figure 16B, the total number of bits on the SLI bus is equal to the sum of the number of bits in the individual SLI bus registers of the eight dual channel LED driver ICs 701A through 701H. Assume that the SLI bus register in each of the eight driver ICs 701A to 701H includes an 8-bit channel first code register, an 8-bit function first code register, and a 16-bit data register. , a total of 32 bits. It takes 256 SCK pulses to write SLI bus data into eight 32-bit shift registers. The first 32 SCK pulses will load the data required by the driver IC 701H, and the 33rd to 64th SCK pulses will load the data required by the driver IC 701G, and so on. Specifically, in the example of FIG. 16B, after the t _latch duration occurs, the data D _B , D _D , D _F , D _H , D _J , D _L , D _{N ,} and D _{Q are} derived from the driver ICs 701A to 701H. The data registers in the SLI bus are respectively copied to their corresponding PWM preload latches PWM B, PWM D, PWM F, PWM H, PWM J, PWM L, PWM N and PWM Q.

Since each driver IC includes two channels with two sets of preload latches, a second broadcast is required on the SLI bus to load the PWM preload latches PWM A, PWM C, PWM E, PWM G, PWM I, PWM K and PWM M. This procedure must be repeated for each set of latches to be loaded.

The operation of a multi-channel multi-latch sequence is further illustrated in the timing and flow diagram of Figure 16C, which shows the output of the interface IC that controls the SLI bus and all satellite LED driver ICs. In the example shown, timing waveforms 801 and 802 represent the SCK clock and the Vsync clock, and the waveform progresses from left to right in time.

During the SCK burst 803A, the first set of PWM duration "D" data is moved to the SLI bus displacement register. At the end of SCK burst 803A, the SCK signal is temporarily held "high" during which time the SLI bus "D" data is copied to the preload latches P, M, K, I, G, E, C. And A. During the next SCK burst 803B, the second set of PWM "D" data is moved to the SLI bus shift register. At the end of SCK burst 803B, the SCK signal is temporarily held "high" during which time the SLI bus "D" data is copied to the preload latches Q, N, L, J, H, F, D. And B.

During the SCK burst 803C and the subsequent SCK "high", the phase data is moved into the SLI bus and latched into the preload latches P, M, K, I, G, E, C and A, followed by SCK bursts 803D and then SCK "high", during which phase data is moved to the SLI sink It is aligned and latched into preload latches Q, N, L, J, H, F, D, and B. Thereafter, during the SCK burst 803E and the subsequent SCK "high", the pixel (ie, LED current) data is moved into the SLI bus and latched to the preload latches P, M, K, I. , G, E, C, and A, followed by SCK burst 803F and subsequent SCK "high", during which the image data is moved to the SLI bus and latched to the preload latches Q, N, L, J, H, F, D and B. Finally, during the SCK burst 803G and the subsequent SCK "high", the fault data is moved into the SLI bus and latched into the preload latches P, M, K, I, G, E, C and A. , followed by SCK burst 803H and subsequent SCK "high", during which the fault data is moved into the SLI bus and latched to the preload latches Q, N, L, J, H, F, D and B.

It should be noted that with respect to the disclosed first code multiplexed SLI bus, the sequence of writing of the first or second channel within a driver IC is completely arbitrary. For example, during SCK 803A, PWM data is used for channels P, M, K, I, G, E, C, and A or for channels Q, N, L, J, H, F, D, and B. difference. Since the data in the preload latch is not displayed until it is copied to the associated latch at Vsync pulse 802, the order in which the preload latch is loaded does not matter. The only requirement is that the data required for the channel (ie, channel P or channel Q) in the driver IC that is the farthest from the interface IC in the daisy chain is written first, and the channel in the driver IC closest to the interface IC (channel) The information required for A or channel B) is last written. In theory, the first and second channels can be mixed in the SLI bus communication instead or in any way (for example, channel Q is followed by channel M and then channel K), but this makes the check sequence more error-free. Difficult and not beneficial.

In the disclosed first code multiplexed SLI bus, the sequence by which the preload latches are loaded into a given driver IC and channel is also completely arbitrary. For example, the preload latch holding the phase data can be loaded before the preload latch holding the PWM action time factor data, and this can be done before or after loading the pixel data or fault data into the preload latch. carry out. Therefore, the first code multiplexed SLI bus and method of the present invention are multi-channel and multi-channel The flexibility of the parameter LED drive provides great flexibility.

At Vsync pulse 802, data from all preload latches is copied into the associated active latch, as indicated by the arrows. Specifically, data for PWM P and PWM Q, phase P and phase Q, pixel P and pixel Q, and fault P and fault Q are written into the active latch of the dual-channel LED driver IC 701H; The data for PWM M and PWM N, phase M and phase N, pixel M and pixel N, and fault M and fault N are written to the active latch of the dual-channel LED driver IC 701G, and so on. Also at Vsync, the PWM data, phase data, pixel data, and fault data for the LED driver IC 701A closest to the interface IC are also copied from the preload latch to the active latch.

Rearrange LED driver status

After the active latches in the LED driver IC are fully loaded, a subset of the data can be sent to update the latches for dynamic changes. A common dynamic change is to update the PWM brightness setting (that is, one of the parameters can be changed with each video frame). This update, shown in the SLI bus data sequence shown in Figure 17A, includes loading two data for all of the PWM preload latches in LED driver ICs 701H through 701A in two data broadcasts from the interface IC. Sequences 851 and 852. The data sequences 851 and 852 are thus a subset of the data sequences shown in FIG.

Blank or "don't care" data may also be moved to the SLI bus displacement register in the channel that does not need to be updated, with the restriction that the first code is selected so as not to be written to the driver IC. Any latch. For example, if only the PWM P and PWM Q latches are changed, the data that is shifted through the SLI bus can include 14 channels of "arbitrary" data and two channels of PWM data, as shown in the data sequence of Figure 17B. By selecting the first code of one of the latches in the unaddressed IC, the "arbitrary" data or DC data in the data field is ignored by selecting one of the channel selection codes or one of the function selection codes. . For example, writing a channel code from 0000 to 0100 or greater (hexadecimal 04) will select One of the four integrated hexadecimal channels 00 to 03 in a four-channel LED driver IC is out of range and will therefore be ignored. Alternatively, writing one of the function select codes from 0000 to 1000 or greater (hexadecimal to 08) will select one of the function latches in the eight latch hexadecimal range 00 to 07 and therefore Will be ignored.

Alternatively, a safe choice is to use the first of the binary codes FFFF, 1111-1111-1111-1111 to select one of the values of all of the implementable latch counts in even the largest system. In an alternate embodiment, the code FFFF can be reserved as a "random" command. This "arbitrary" function is necessary because in the communication protocol based on a displacement register, the correct number of bits must be shifted to move the updated data to the first code of the SLI bus in the appropriate driver IC. In the device and data register. Referring to the example shown in FIG. 17B, the 32-bit block loaded into the channel 701H, which contains one of the updated data for the PWM P, needs to be seven after the updated 32-bit block containing the PWM P-Latch. A 32-bit block or 224 bits are moved to the shift register. The same is true in PWM Q, where one of the first codes of the selected Q channel and PWM function latches, the 32-bit update block must be connected after 224 bits to move the data to its corresponding driver IC. 701H. It should be reiterated that in a two-channel driver IC, there is no difference in whether the second channel in the overall LED driver system is channels B, D, F, H, J, L, N, and Q. Therefore, moving the correct number of bits into the SLI bus after moving the update data for a particular latch onto the SLI bus is important for selecting the correct channel, function, and LED driver IC system.

Finally, as long as the number of bits of the broadcast is equal to the number of LED driver ICs multiplied by the number of bits in the SLI bus register of each driver IC, the update can be mixed in a single SLI bus update.

For example, in the SLI bus communication sequence of FIG. 17C, a mix of PWM, fault, phase, and DC data is transmitted in the broadcast sequence 891, including a total of 8 channels multiplied by 32 bits on the SLI bus. Or 256 bits. In the example shown, not only are the different functions mixed together into the same data stream, but the selected channel can also be connected to the A channel and the B channel. Road data is mixed into the same data stream. For example, the "A channel" data includes PWM C, phase G, and PWM P data for the LED driver ICs 701B, 701D, and 701H, respectively, and the "B channel" data includes faults for the corresponding LED driver ICs 701E and 701G. The J data and PWM N data, and the data in the driver ICs 701A, 701C and 701F indicate a "casual" drive state. In short, in the embodiments described above, data for up to one (but no more than one) of the preload latches in any of the driver ICs can be included in any single loaded into the SLI bus. In the data sequence.

In the manner specified, the LED code state can be updated using the disclosed first code multiplex SLI bus protocol without resending the full set of latch information.

SLI busbar flexibility

The disclosed first code multiplexed SLI bus and various functions not specifically disclosed herein (including the ability to switch a given channel on or off, the ability to invert the PWM signal, and encode the CSFB feedback signal and embed it into The capabilities in the SLI bus protocol are compatible. Therefore, the applications and functions described in this disclosure should not be construed in any way as limiting the utility of the SLI bus.

81A‧‧‧LED Driver IC

81H‧‧‧LED Driver IC

83A‧‧‧LED string

83B‧‧‧LED string

83P‧‧‧LED string

83Q‧‧‧LED string

85A‧‧‧ analog control and sensing circuit

85H‧‧‧ analog control and sensing circuit

86A‧‧‧I Precision Gate Driver Circuit

86B‧‧‧I Precision Gate Driver Circuit

86P‧‧‧I Precision Gate Driver Circuit

86Q‧‧‧I Precision Gate Driver Circuit

87A‧‧‧ Current Slot DMOSFET

87B‧‧‧ Current Slot DMOSFET

87P‧‧‧ Current Slot DMOSFET

87Q‧‧‧ Current Slot DMOSFET

88A‧‧‧Integrated HV diode

88B‧‧‧Integrated HV diode

88P‧‧‧Integrated HV diode

88Q‧‧‧Integrated HV diode

89A‧‧‧Digital Control and Timing Circuit

89H‧‧‧Digital Control and Sequencing Circuit

90A‧‧‧Sequence lighting interface bus

90H‧‧‧Sequence lighting interface bus

100‧‧‧Distributed multi-channel LED backlight driver system

101‧‧‧Intermediate area circuit (IC)

102‧‧‧ capacitor

107‧‧‧Common signal line

108‧‧‧Switch mode power supply

109‧‧‧ line

110‧‧‧Fixed +24V supply rail

111‧‧‧ Current feedback signal

112B‧‧‧CSFB line

112H‧‧‧CSFB line

112I‧‧‧CSFB line

113A‧‧‧ signal line

113B‧‧‧ signal line

113H‧‧‧ signal line

113I‧‧‧ signal line

122‧‧‧Sequence peripheral interface bus

123‧‧‧Sequence illumination interface unit / sequence illumination interface circuit

124‧‧‧Sequence and Control Unit

125‧‧‧Voltage Reference Source

126‧‧‧ bias supply unit

127‧‧‧Operation transconductance amplifier

CSFBI‧‧‧current sensing feedback input pin

CSFBO‧‧‧current sensing feedback output pin

FLT‧‧‧Digital Fault Line/Fault Interrupt Line

GSC‧‧‧ digital clock line

SCK‧‧‧ digital clock line

SI‧‧‧Sequence input/pin

SO‧‧‧Sequence output/pin

Vcc‧‧‧ power supply

Vref‧‧‧ analog reference voltage signal line

Vsync‧‧‧ digital clock line

Claims (18)

A method of controlling a plurality of light emitting diode (LED) strings in a video display, each of the LED strings being associated with a channel, the method comprising: identifying digital data of one of the channels Shifting into a channel first code register; shifting a function digit data identifying the one of the channels to a function first code register; indicating the one of the channels in the one of the channels The digital data of one of the functions is shifted into a data buffer; and by copying the data from the data buffer to a preload latch at a first rate and by being less than the first rate A second rate copies the data from the preload latch to an active latch, using the data identifying the one of the channels and identifying the data for the function in the one of the channels to This value of the function is applied to one of the LED strings associated with the one of the channels. The method of claim 1, further comprising: shifting the digital data through the plurality of channel first code registers, the plurality of function first code registers, and the plurality of data registers to control the plurality of LED strings. The method of claim 2, wherein the channel first code register, the function first code register, and the data registers are connected in series by a daisy chain. The method of claim 3, wherein the daisy chain begins and ends at an interface IC, such that when data is transmitted through the first code register of the channels, the function first code register, and the data registers are displaced The data is shifted back to the interface IC. The method of claim 4, wherein the first channel first code register, a first function first The code register and a first data register are associated with a channel of the first group, and a second channel first code register, a second function first code register and a second data temporary The memory system is associated with a channel of a second group. The method of claim 5, wherein the first channel first code register, the first function first code register, and the first data register are included in a first LED driver IC, and the second The channel first code register, the second function first code register and the second data register are included in a second LED driver IC. The method of claim 3, wherein the channel first code register, the function first code register, and the data register are formed in a plurality of LED driver ICs, each of the plurality of LED driver ICs One includes a channel first code register, a function first code register and a data register. The method of claim 1, wherein the function comprises at least one of a time factor of one of a switch connected to one of the LED strings, a phase delay of one of the switches, and a magnitude of current through one of the LED strings. The method of claim 1, wherein the function comprises a definition of a fault condition comprising one or more of an open LED, a shorted LED, and an over temperature condition. The method of claim 1, wherein the using the data further comprises: copying the data from the preload latch to the active latch in synchronization with a synchronization signal, the synchronization signal defining a frame rate of the video display. The method of claim 1, further comprising: shifting the digital data through a plurality of channel first code registers, a plurality of function first code registers, and a plurality of data registers to control a plurality of the plurality of LED strings Features. The method of claim 11, further comprising the function of associating a group of LED strings associated with a group of the plurality of LED strings during an initialization phase The data is shifted into the data registers. The method of claim 1, wherein the video display is a television. The method of claim 1, wherein the video display is a liquid crystal display. A method of controlling a function of a plurality of light emitting diode (LED) strings in a video display, each of the LED strings being associated with a channel, the method comprising: data representing a value of a function Loading into a data register in each channel of a group of channels; and copying the data representing the value from the data buffer to a preload latch by a first rate And by copying the data representing the value from the preload latch to an active latch at a second rate less than the first rate, using the representation in each channel of the group of channels The data of the value of the function is to apply the value of the function to each LED string associated with each channel of the channel of the group. A light emitting diode (LED) driver system comprising: one or more LED strings in a video display, each of the one or more LED strings being associated with a channel; a sequence of illumination interfaces (SLI a bus bar comprising a channel first code register, a function register, a data register and an input for receiving data identifying one of the channels, identifying the one of the channels Information of a function and data representing a value of the function in the one of the channels, the SLI bus is configured to shift the received data identifying the one of the channels to a channel first code temporary Storing, in the memory, the received data identifying the function in the one of the channels into the function register and the value representing the function in the one of the channels Receiving data into the data register; and a digital control and timing circuit coupled between at least one of the one or more LED strings and the SLI bus, the digital control and timing circuit including a preload latch and an active latch And constructing the data buffer from the SLI bus at a first rate to copy the data to the preload latch and copying the preload latch from the preload latch at a second rate less than the first rate Data to the active latch. The LED driver system of claim 16, wherein each of the channel first code register and the function register comprises an 8-bit register and the data register comprises a 16-bit register. The LED driver system of claim 16, further comprising one of the interface ICs coupled to the SLI bus.